We develop the concepts of recursively nowhere dense sets and sets that are recursively of first category and study closed sets of points in light of Baire's Category Theorem. Our theorems are primarily concerned with exdomains of recursive quantum functions and hence with avoidable points . An avoidance function is a recursive function which can be used to expel avoidable points from domains of recursive quantum functions. We define an avoidable set of points to be an (...) arbitrary subset of the avoidable points of a single avoidance function, and we study an effective union of such sets which we call a piecemeal avoidable set. We note that each of ‘the set of recursive points’ and ‘the set of avoidable points’ is of first category but not recursively of first category. We show an exdomain exists which is recursively nowhere dense, as well as one that is nowhere dense but not recursively nowhere dense. After establishing that every exdomain is recursively of first category, we prove that given any fixed exdomain, there is another exdomain, which while dense in the underlying space, is disjoint from the fixed exdomain. Finally, we show how to build a recursive sequence of recursive quantum functions that have mutually disjoint, dense exdomains. (shrink)

In [5], Metakides and Nerode introduced the study of recursively enumerable substructures of a recursively presented structure. The main line of study presented in [5] is to examine the effective content of certain algebraic structures. In [6], Metakides and Nerode studied the lattice of r.e. subspaces of a recursively presented vector space. This lattice was later studied by Kalantari, Remmel, Retzlaff and Shore. Similar studies have been done by Metakides and Nerode [7] for algebraically closed fields, by (...) Remmel [10] for Boolean algebras and by Metakides and Remmel [8] and [9] for orderings. Kalantari and Retzlaff [4] introduced and studied the lattice of r.e. subsets of a recursively presented topological space. Kalantari and Retzlaff consideredX, a topological space with ⊿, a countable basis. This basis is coded into integers and with the help of this coding, r.e. subsets ofωgive rise to r.e. subsets ofX. The notion of “recursiveness” of a topological space is the natural next step which gives rise to the question of what should be the “degree” of an r.e. open subset ofX? It turns out that any r.e. open set partitions ⊿; into four sets whose Turing degrees become central in answering the question raised above.In this paper we show that the degrees of the elements of the partition of ⊿ imposed by an r.e. open set can be “controlled independently” in a sense to be made precise in the body of the paper. In [4], Kalantari and Retzlaff showed that givenAany r.e. set andany r.e. open subset ofX, there exists an r.e. open set ℋ which is a subset ofand is dense in and in whichAis coded. This shows that modulo a nowhere dense set, an r.e. open set can become as complicated as desired. After giving the general technical and notational machinery in §1, and giving the particulars of our needs in §2, in §3 we prove that the set ℋ described above could be made to be precisely of degree ofA. We then go on and establish various results on the mentioned partitioning of ⊿. One of the surprising results is that there are r.e. open sets such that every element of partitioning of ⊿ is of a different degree. Since the exact wording of the results uses the technical definitions of these partitioning elements, we do not summarize the results here and ask the reader to examine §3 after browsing through §§1 and 2. (shrink)

This paper is an investigation of definability hierarchies on effective topological spaces. An open subset U of an effective space X is definable iff there is a parameter free definition φ of U so that the atomic predicate symbols of φ are recursively open relations on X . The complexity of a definable open set may be identified with the quantifier complexity of its definition. For example, a set U is an ∃∃∀∃-set if it has an ∃∃∀∃ parameter free (...) definition using only recursively open predicate symbols. Since X is not equipped with a natural pairing apparatus such a U need not be an ∃∀∃-set. Let Σ denote the class of all ∃-sets, ∃∃-sets, ∃∃∃-sets etc. We show that an open set is in Σ iff it is equivalent modulo a nowhere dense set to a recursively enumerable open set . Thus Σ = e.r.e. Indeed we show the existence of a universal Σ -set as well as the existence of universal sets for higher levels of the definability hierarchy. (shrink)

We consider the infinite game where player ONE chooses terms of a strictly increasing sequence of first category subsets of a space and TWO chooses nowhere dense sets. If after ω innings TWO's nowhere dense sets cover ONE's first category sets, then TWO wins. We prove a theorem which implies for the real line: If TWO has a winning strategy which depends on the most recent n moves of ONE only, then TWO has a winning strategy (...) depending on the most recent 3 moves of ONE (Corollary 3). Our results give some new information concerning Problem 1 of [S1] and clarifies some of the results in [B-J-S] and in [S1]. (shrink)

An analogue of Mathias forcing is studied in connection of free Boolean algebras and nowhere dense ultrafilters. Some applications to rigid Boolean algebras are given.

A set A of vertices of a graph G is called d-scattered in G if no two d-neighborhoods of (distinct) vertices of A intersect. In other words, A is d-scattered if no two distinct vertices of A have distance at most 2d. This notion was isolated in the context of finite model theory by Ajtai and Gurevich and recently it played a prominent role in the study of homomorphism preservation theorems for special classes of structures (such as minor closed classes). (...) This in turn led to the notions of wide, almost wide and quasi-wide classes of graphs. It has been proved previously that minor closed classes and classes of graphs with locally forbidden minors are examples of such classes and thus (relativized) homomorphism preservation theorem holds for them. In this paper we show that (more general) classes with bounded expansion and (newly defined) classes with bounded local expansion and even (very general) nowhere dense classes are quasi wide. This not only strictly generalizes the previous results but it also provides new proofs and algorithms for some of the old results. It appears that bounded expansion and nowhere dense classes are perhaps a proper setting for investigation of wide-type classes as in several instances we obtain a structural characterization. This also puts classes of bounded expansion in the new context. Our motivation stems from finite dualities. As a corollary we obtain that any homomorphism closed first order definable property restricted to a bounded expansion class is a restricted duality. (shrink)

We prove that there is a -ideal of compact sets which is strictly above in the Tukey order. Here is the collection of all compact nowhere dense subsets of the Cantor set. This answers a question of Louveau and Veličković asked in [Alain Louveau, Boban Veličković, Analytic ideals and cofinal types, Ann. Pure Appl. Logic 99 171–195].

For a Polish group let be the minimal number of translates of a fixed closed nowhere dense subset of required to cover . For many locally compact this cardinal is known to be consistently larger than which is the smallest cardinality of a covering of the real line by meagre sets. It is shown that for several non-locally compact groups . For example the equality holds for the group of permutations of the integers, the additive group of a (...) separable Banach space with an unconditional basis and the group of homeomorphisms of various compact spaces. (shrink)

We study some properties of the quotient forcing notions \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${Q_{tr(I)} = \wp(2^{< \omega})/tr(i)}$$\end{document} and PI = B(2ω)/I in two special cases: when I is the σ-ideal of meager sets or the σ-ideal of null sets on 2ω. We show that the remainder forcing RI = Qtr(I)/PI is σ-closed in these cases. We also study the cardinal invariant of the continuum \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathfrak{h}_{\mathbb{Q}}}$$\end{document}, the distributivity (...) number of the quotient \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${Dense(\mathbb{Q})/nwd}$$\end{document}, in order to show that \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\wp(\mathbb{Q})/nwd}$$\end{document} collapses \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathfrak{c}}$$\end{document} to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathfrak{h}_{\mathbb{Q}}}$$\end{document}, thus answering a question addressed in Balcar et al. (Fundamenta Mathematicae 183:59–80, 2004). (shrink)

The structure Dense /nwd and gaps in analytic quotients of equation image have been studied in the literature 2, 3, 1. We prove that the structures Dense /nwd and equation image have gaps of type equation image, and there are no -gaps for equation image, where equation image is the additivity number of the meager ideal. We also prove the existence of -gaps in these structures. Finally we characterize the cofinality of the meager ideal equation image using families (...) of sets in Dense /nwd. (shrink)

R. Shore proved that every recursively enumerable set can be split into two nowhere simple sets. Splitting theorems play an important role in recursion theory since they provide information about the lattice ϵ of all r. e. sets. Nowhere simple sets were further studied by D. Miller and J. Remmel, and we generalize some of their results. We characterize r. e. sets which can be split into two effectively nowhere simple sets, and r. e. sets which (...) can be split into two r. e. non-nowhere simple sets. We show that every r. e. set is either the disjoint union of two effectively nowhere simple sets or two noneffectively nowhere simple sets. We characterize r. e. sets whose every nontrivial splitting is into nowhere simple sets, and r. e. sets whose every nontrivial splitting is into effectively nowhere simple sets. R. Shore proved that for every effectively nowhere simple set A, the lattice L* is effectively isomorphic to ϵ*, and that there is a nowhere simple set A such that L* is not effectively isomorphic to ϵ*. We prove that every nonzero r. e. Turing degree contains a noneffectively nowhere simple set A with the lattice L* effectively isomorphic to ϵ*. (shrink)

We investigate cardinal invariants related to the structure of dense sets of rationals modulo the nowhere dense sets. We prove that , thus dualizing the already known [B. Balcar, F. Hernández-Hernández, M. Hrušák, Combinatorics of dense subsets of the rationals, Fund. Math. 183 59–80, Theorem 3.6]. We also show the consistency of each of and . Our results answer four questions of Balcar, Hernández and Hrušák [B. Balcar, F. Hernández-Hernández, M. Hrušák, Combinatorics of dense subsets (...) of the rationals, Fund. Math. 183 59–80, Questions 3.11]. (shrink)

The complexity of equivalence relations has received much attention in the recent literature. The main tool for such endeavour is the following reducibility: given equivalence relations R and S on natural numbers, R is computably reducible to S if there is a computable function f:ω→ω that induces an injective map from R-equivalence classes to S-equivalence classes. In order to compare the complexity of equivalence relations which are computable, researchers considered also feasible variants of computable reducibility, such as the polynomial-time reducibility. (...) In this work, we explore Peq, the degree structure generated by primitive recursive reducibility on primitive recursive equivalence relations with infinitely many equivalence classes. In contrast with all other known degree structures on equivalence relations, we show that Peq has much more structure: e.g., we show that it is a dense distributive lattice. On the other hand, we also offer evidence of the intricacy of Peq, proving, e.g., that the structure is neither rigid nor homogeneous. (shrink)

The structure \documentclass{article}\usepackage{amssymb}\begin{document}\pagestyle{empty}$\mathrm{Dense}(\mathbb {Q})/\mathbf {nwd}$\end{document} and gaps in analytic quotients of \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$\mathscr {P}(\omega )$\end{document} have been studied in the literature 2, 3, 1. We prove that the structures \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$\mathrm{Dense}(\mathbb {Q})/\mathbf {nwd}$\end{document} and \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$\mathscr {P}(\mathbb {Q})/\mathbf {nwd}$\end{document} have gaps of type \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$(\mathrm{add}( \mathscr {M}), \omega )$\end{document}, and there are no (λ, ω)-gaps for \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$\lambda < \mathrm{add}(\mathscr {M})$\end{document}, where \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$\mathrm{add}(\mathscr {M})$\end{document} is the additivity number of the meager ideal. We also prove the existence of (ω1, ω1)-gaps in these structures. Finally we (...) characterize the cofinality of the meager ideal \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$\mathrm{cof}(\ mathscr {M})$\end{document} using families of sets in \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$\mathrm{Dense}(\mathbb {Q})/\mathbf {nwd}$\end{document}. (shrink)

We study topological constructions in the recursion theoretic framework of the lattice of recursively enumerable open subsets of a topological space X. Various constructions produce complemented recursively enumerable open sets with additional recursion theoretic properties, as well as noncomplemented open sets. In contrast to techniques in classical topology, we construct a disjoint recursively enumerable collection of basic open sets which cannot be extended to a recursively enumerable disjoint collection of basic open sets whose union is (...) class='Hi'>dense in X. (shrink)

In the present paper we prove that the isolated differences of r. e. degrees are dense in the r. e. degrees.

In [Countable thin [Formula: see text] classes, Ann. Pure Appl. Logic 59 79–139], Cenzer, Downey, Jockusch and Shore proved the density of degrees containing members of countable thin [Formula: see text] classes. In the same paper, Cenzer et al. also proved the existence of degrees containing no members of thin [Formula: see text] classes. We will prove in this paper that the c.e. degrees containing no members of thin [Formula: see text] classes are dense in the c.e. degrees. We (...) will also prove that the c.e. degrees containing members of thin [Formula: see text] classes are dense in the c.e. degrees, improving the result of Cenzer et al. mentioned above. Thus, we obtain a new natural subclass of c.e. degrees which are both dense and co-dense in the c.e. degrees, while the other such class is the class of branching c.e. degrees 113–130] for nonbranching degrees and [T. A. Slaman, The density of infima in the recursively enumerable degrees, Ann. Pure Appl. Logic 52 155–179] for branching degrees). (shrink)

We consider questions related to the rigidity of the structure R, the PTIME-Turing degrees of recursive sets of strings together with PTIME-Turing reducibility, pT, and related structures; do these structures have nontrivial automorphisms? We prove that there is a nontrivial automorphism of an ideal of R. This can be rephrased in terms of partial relativizations. We consider the sets which are PTIME-Turing computable from a set A, and call this class PTIMEA. Our result can be stated as follows: There is (...) an oracle, A, relative to which the PTIME-Turing degrees are not rigid . Furthermore, the automorphism can be made to preserve the complexity classes DTIMEA for all k 1, or to move any DTIMEA for n 2. From the existence of such an automorphism we conclude as a corollary that there is an oracle A relative to which the classes DTIME are not definable over R. We carry out the corresponding partial relativization for the many-one degrees to construct an oracle, A, relative to which the PTIMA-many-one degrees relative to A have a nontrivial automorphism, and one relative to which the lattice of sets in PTIMEA under inclusion have a nontrivial automorphism. The proof is phrased as a forcing argument; we construct the set A to meet a particular collection of dense sets in our notion of forcing. Roughly, the dense sets will guarantee that if A meets these sets and we split A into two pieces, A0 and A1, in a simple way, and then switching the roles of A0 and A1 in all computations from A will produce an automorphism of the ideal of PTIMA-degrees below A. We force A0 and A1 to have different PTIME-Turing degree; this will then make the automorphism nontrivial. An appropriately generic set A is constructed using a priority argument. (shrink)

Abstract. Traditional epistemology of knowledge and belief can be succinctly characterized as JTB-epistemology, i.e., it is characterized by the thesis that knowledge is justified true belief. Since Gettier’s trail-blazing paper of 1963 this account has become under heavy attack. The aim of is paper is to study the Gettier problem and related issues in the framework of topological epistemic logic. It is shown that in the framework of topological epistemic logic Gettier situations necessarily occur for most topological models of knowledge (...) and belief. On the other hand, there exists a special class of topological models (based on so called nodec spaces) for which traditional JTB-epistemology is valid. Further, it is shown that for each topological model of Stalnaker’s combined logic KB of knowledge and belief a canonical JTB-model (its JTB-doppelganger) can be constructed that shares many structural properties with the original model but is free of Gettier situations. The topological model and its JTB-doppelganger both share the same justified belief operator and have very similar knowledge operators. Seen from a somewhat different perspective, the JTB-account of epistemology amounts to a simplification of a more general epistemological account of knowledge and belief that assumes that these two concepts may differ in some cases. The JTB-account of knowledge and belief assumes that the epistemic agent’s cognitive powers are rather large. Thereby in the JTB-epistemology Gettier cases do not occur. Eventually, it is shown that for all topological models of Stalnaker’s KB-logic Gettier situations are topologically characterized as nowhere dense situations. This entails that Gettier situations are epistemologically invisible in the sense that they can neither be known nor believed with justification with respect to the knowledge operator and the belief operator of the models involved. (shrink)

A maximal almost disjoint (mad) family $\mathscr{A} \subseteq [\omega]^\omega$ is Cohen-stable if and only if it remains maximal in any Cohen generic extension. Otherwise it is Cohen-unstable. It is shown that a mad family, A, is Cohen-unstable if and only if there is a bijection G from ω to the rationals such that the sets G[A], A ∈A are nowhere dense. An ℵ 0 -mad family, A, is a mad family with the property that given any countable family (...) $\mathscr{B} \subset [\omega]^\omega$ such that each element of B meets infinitely many elements of A in an infinite set there is an element of A meeting each element of B in an infinite set. It is shown that Cohen-stable mad families exist if and only if there exist ℵ 0 -mad families. Either of the conditions b = c or $\mathfrak{a} ) implies that there exist Cohen-stable mad families. Similar results are obtained for splitting families. For example, a splitting family, S, is Cohen-unstable if and only if there is a bijection G from ω to the rationals such that the boundaries of the sets G[S], S ∈S are nowhere dense. Also, Cohen-stable splitting families of cardinality ≤ κ exist if and only if ℵ 0 -splitting families of cardinality ≤ κ exist. (shrink)

We discuss saturating ultrafilters on N, relating them to other types of nonprincipal ultrafilter. (a) There is an (ω,c)-saturating ultrafilter on $\mathbf{N} \operatorname{iff} 2^\lambda \leq \mathfrak{c}$ for every $\lambda and there is no cover of R by fewer than c nowhere dense sets. (b) Assume Martin's axiom. Then, for any cardinal κ, a nonprincipal ultrafilter on N is (ω,κ)-saturating iff it is almost κ-good. In particular, (i) p(κ)-point ultrafilters are (ω,κ)-saturating, and (ii) the set of (ω,κ)-saturating ultrafilters is (...) invariant under homeomorphisms of $\beta\mathbf{N\backslash N}$ . (c) It is relatively consistent with ZFC to suppose that there is a Ramsey p(c)-point ultrafilter which is not (ω,c)-saturating. (shrink)

We prove that every countably determined set C is U-meager if and only if every internal subset A of C is U-meager, provided that the cofinality and coinitiality of the cut U are both uncountable. As a consequence we prove that for such cuts a countably determined set C which intersects every U-monad in at most countably many points is U-meager. That complements a similar result in [KL]. We also give some partial solutions to some open problems from [KL]. We (...) prove that the set K = {1,...,H}, where H is an infinite integer, cannot be expressed as a countable union of countably determined sets each of which is U-meager for some cut U with min{cf (U), ci (U)} ≥ ω1. Also, every Borel, Σ1 m or countably determined set C which is U-meager for every cut U is a countable union of Borel, Σ1 m or countably determined sets respectively, which are U-nowhere dense for every cut U. Further, the class of Borel U-meager sets for min{cf(U), ci(U)} ≥ ω1 coincides with the least family of sets containing internal U-meager sets and closed with respect to the operation of countable union and intersection. The same is true if the phrase "U-meager sets" is replaced by "U-meager for every cut U.". (shrink)

We study the uniform computational content of different versions of the Baire category theorem in the Weihrauch lattice. The Baire category theorem can be seen as a pigeonhole principle that states that a complete metric space cannot be decomposed into countably many nowhere dense pieces. The Baire category theorem is an illuminating example of a theorem that can be used to demonstrate that one classical theorem can have several different computational interpretations. For one, we distinguish two different logical (...) versions of the theorem, where one can be seen as the contrapositive form of the other one. The first version aims to find an uncovered point in the space, given a sequence of nowhere dense closed sets. The second version aims to find the index of a closed set that is somewhere dense, given a sequence of closed sets that cover the space. Even though the two statements behind these versions are equivalent to each other in classical logic, they are not equivalent in intuitionistic logic, and likewise, they exhibit different computational behavior in the Weihrauch lattice. Besides this logical distinction, we also consider different ways in which the sequence of closed sets is “given.” Essentially, we can distinguish between positive and negative information on closed sets. We discuss all four resulting versions of the Baire category theorem. Somewhat surprisingly, it turns out that the difference in providing the input information can also be expressed with the jump operation. Finally, we also relate the Baire category theorem to notions of genericity and computably comeager sets. (shrink)

Traditional epistemology of knowledge and belief can be succinctly characterized as JTB-epistemology, i.e., it is characterized by the thesis that knowledge is justified true belief. Since Gettier’s trail-blazing paper of 1963 this account has become under heavy attack. The aim of is paper is to study the Gettier problem and related issues in the framework of topological epistemic logic. It is shown that in the framework of topological epistemic logic Gettier situations necessarily occur for most topological models of knowledge and (...) belief. On the other hand, there exists a special class of topological models (based on so called nodec spaces) for which traditional JTB-epistemology is valid. Further, it is shown that for each topological model of Stalnaker’s combined logic KB of knowledge and belief a canonical JTB-model (its JTB-doppelganger) can be constructed that shares many structural properties with the original model but is free of Gettier situations. The topological model and its JTB-doppelganger both share the same justified belief operator and have very similar knowledge operators. Seen from a somewhat different perspective, the JTB-account of epistemology amounts to a simplification of a more general epistemological account of knowledge and belief that assumes that these two concepts may differ in some cases. The JTB-account of knowledge and belief assumes that the epistemic agent’s cognitive powers are rather large. Thereby in the JTB-epistemology Gettier cases do not occur. Eventually, it is shown that for all topological models of Stalnaker’s KB- logic Gettier situations are topologically characterized as nowhere dense situations. This entails that Gettier situations are epistemologically invisible in the sense that they can neither be known nor believed with justification with respect to the knowledge operator and the belief operator of the models involved. Keywords. Stalnaker’s logic KB of knowledge and belief; Topological epistemology; Epistemic Invisibility; Doxastic invisibility; Gettier cases; . (shrink)

It is proved that the following conditions are equivalent: (a) there exists a complete, atomless, σ-centered Boolean algebra, which does not contain any regular, atomless, countable subalgebra, (b) there exists a nowhere dense ultrafilter on ω. Therefore, the existence of such algebras is undecidable in ZFC. In "forcing language" condition (a) says that there exists a non-trivial σ-centered forcing not adding Cohen reals.

A completely mitotic computably enumerable degree is a c.e. degree in which every c.e. set is mitotic, or equivalently in which every c.e. set is autoreducible. There are known to be low, low2, and high completely mitotic degrees, though the degrees containing non-mitotic sets are dense in the c.e. degrees. We show that there exists an upper cone of c.e. degrees each of which contains a non-mitotic set, and that the completely mitotic c.e. degrees are nowhere dense (...) in the c.e. degrees. We also show that there is a set computably enumerable in and above 0′ which is not the jump of any completely mitotic degree. (shrink)

Let κ be a regular cardinal and P a partial ordering preserving the regularity of κ. If P is (κ-Baire and) of density κ, then there is a mad family on κ killed in all generic extensions (if and) only if below each p∈P there exists a κ-sized antichain. In this case a mad family on κ is killed (if and) only if there exists an injection from κ onto a dense subset of Ult(P) mapping the elements of onto (...) nowhere dense sets. If 2< κ =κ, then in each generic extension of V, in which κ is the minimal cardinal obtaining new subsets, some mad family on κ is killed or an independent subset of κ appears. Also, the κ-Suslin Hypothesis holds iff there exists a mad family on κ which is killed in each generic extension containing new subsets of κ and preserving P(λ) for λ<κ. (shrink)

According to [M.S. Kurilić, Cohen-stable families of subsets of the integers, J. Symbolic Logic 66 257–270], adding a Cohen real destroys a splitting family on ω if and only if is isomorphic to a splitting family on the set of rationals, , whose elements have nowhere dense boundaries. Consequently, implies the Cohen-indestructibility of . Using the methods developed in [J. Brendle, S. Yatabe, Forcing indestructibility of MAD families, Ann. Pure Appl. Logic 132 271–312] the stability of splitting families (...) in several forcing extensions is characterized in a similar way . Also, it is proved that a splitting family is preserved by the Sacks forcing if and only if it is preserved by some forcing which adds a new real. The corresponding hierarchy of splitting families is investigated. (shrink)

Let κ B be the least cardinal for which the Baire category theorem fails for the real line R. Thus κ B is the least κ such that the real line can be covered by κ many nowhere dense sets. It is shown that κ B cannot have countable cofinality. On the other hand it is consistent that the corresponding cardinal for 2 ω 1 be ℵ ω . Similar questions are considered for the ideal of measure zero (...) sets, other ω 1 saturated ideals, and the ideal of zero-dimensional subsets of R ω 1. (shrink)

This paper studies the metric structure of the space Hr of absolutely summable sequences of real numbers with at most r nonzero terms. Hr is complete, and is located and nowhere dense in the space of all absolutely summable sequences. Totally bounded and compact subspaces of Hr are characterized, and large classes of located, totally bounded, compact, and locally compact subspaces are constructed. The methods used are constructive in the strict sense. MSC: 03F65, 54E50.

For a subset A of a Polish group G, we study the (almost) packing index pack( A) (respectively, Pack( A)) of A, equal to the supremum of cardinalities |S| of subsets $S\subset G$ such that the family of shifts $\{xA\}_{x\in S}$ is (almost) disjoint (in the sense that $|xA\cap yA|<|G|$ for any distinct points $x,y\in S$). Subsets $A\subset G$ with small (almost) packing index are large in a geometric sense. We show that $\pack}(A)\in\mathbb{N}\cup\{\aleph_0,\mathfrak{c}\}$ for any σ-compact subset A of a (...) Polish group. In each nondiscrete Polish Abelian group G we construct two closed subsets $A,B\subset G$ with $\mathrm{pack}(A)=\mathrm{pack}(B)=\mathfrak{c}$ and \mathrm{Pack}(A\cup B)=1 and then apply this result to show that G contains a nowhere dense Haar null subset $C\subset G$ with pack(C)=Pack(C)=κ for any given cardinal number $\kappa\in[4,\mathfrak{c}]$. (shrink)

In this article we find some sufficient and some necessary ${\Sigma^1_1}$ -conditions with oracles for a model to be resplendent or chronically resplendent. The main tool of our proofs is internal arguments, that is analogues of classical theorems and model-theoretic constructions conducted inside a model of first-order Peano Arithmetic: arithmetised back-and-forth constructions and versions of the arithmetised completeness theorem, namely constructions of recursively saturated and resplendent models from the point of view of a model of arithmetic. These internal arguments (...) are used in conjunction with Pabion’s theorem that ensures that certain oracles are coded in a sufficiently saturated model of arithmetic. Examples of applications are provided for the theories of dense linear orders and of discrete linear orders. These results are then generalised to other ω-categorical theories and theories with a unique countable recursively saturated model. (shrink)

We study the role the axiom of choice plays in the existence of some special subsets of ℝ and its power set ℘.

Contents: Recursive Enumerability and the Jump Operator; On the Degrees Less Than 0'; A Simple Set Which Is Not Effectively Simple; The Recursively Enumerable Degrees Are Dense; Metarecursive Sets (with G Kreisel); Post's Problem, Admissible Ordinals and Regularity; On a Theorem of Lachlan and Marlin; A Minimal Hyperdegree (with R O Gandy); Measure-Theoretic Uniformity in Recursion Theory and Set Theory; Forcing with Perfect Closed Sets; Recursion in Objects of Finite Type; The a-Finite Injury Method (with S G Simpson); (...) Remarks Against Foundational Activity; Countable Admissible Ordinals and Hyperdegrees; The 1-Section of a Type n Object; The k-Section of a Type n Object; Post's Problem, Absoluteness and Recursion in Finite Types; Effective Bounds on Morley Rank; On the Number of Countable Models; Post's Problem in E-Recursion; The Limits of E-Recursive Enumerability; Effective Versus Proper Forcing. (shrink)

By taking a closer look at the construction of an Ackermann function we see that between any primitive recursive degree and its Ackermann modification there is a dense chain of primitive recursive degrees.

continent. 2.1 (2012): 22–28. Jeroen Mettes burst onto the Dutch poetry scene twice. First, in 2005, when he became a strong presence on the nascent Dutch poetry blogosphere overnight as he embarked on his critical project Dichtersalfabet (Poet’s Alphabet). And again in 2011, when to great critical acclaim (and some bafflement) his complete writings were published – almost five years after his far too early death. 2005 was the year in which Dutch poetry blogging exploded. That year saw the foundation (...) of the influential, polemical, and populistically inclined weblog De Contrabas (The Double Bass), which became a strong force for internet poetry in Dutch in the years to follow. In the summer of that year, a lively debate raged in the aftermath of Bas Belleman’s article “ Doet poëzie er nu eindelijk toe ?” (“Does poetry finally matter now?”), on a blog specifically devoted to this question. Up to that point, the poetical debate in the Netherlands had largely been confined to literary reviews (which were often subsidized), having become mostly marginalized in more mainstream media, where poetry could be covered by only a small number of so-called authorities. As a result, literary debate had acquired a rather placid quality. Though a variety of camps with different aesthetics could be discerned, most poetical positions shared a general acceptance of poetry as a form of art somewhat apart from fundamental political concerns. Late modernists would pursue subtlety and density of reference. Others would insist poetry was best understood as a form of entertainment that should ideally be accessible and work well on the stage. Still others would insist that poetry is mostly a play with forms. Linguistically disruptive strategies were valued highly by some, but mostly for their aesthetic effect. Values of disinterested playfulness reigned supreme everywhere. Any idea that poetry could be a field in which one confronts politics and the world was decidedly marginal. This led to a climate in which most attempts at polemics were DOA, often based on far too superficial positioning and analysis. The greatest polemical debates were revolving around the question of whether poetry should be difficult or easy, with both camps defining their ideas of difficulty and accessibility in ways that were so utterly shallow as to make the entire point moot. Debates were performed, rather than engaged with. It was a postmodern hell of underarticulated poetics. Half-consciously, people were yearning for new forms of criticism that could put the oomph back into poetry. Weblogs provided for ways to explore debate directly outside of the clotted older channels of the reviews and the newspapers. Belleman’s essay and the resulting online activity had shown that there was a widespread eagerness to take poetry more seriously as a social art form. It was in this environment that Mettes started his remarkable project Dichtersalfabet . At that moment, Mettes was active mostly in academic circles, having become noted at Leiden University as a particularly gifted student of literary theory. Within the Netherlands, the field of literary theory has a very odd relationship to literature as it is practiced in the country. Academic theory tends to have a mostly international view and engage with international debates of cultural criticism, literary theory, and philosophy, with academics often publishing in English and attending conferences around the world. Literature itself however is much more concerned with domestic traditions. Consequently, in the Netherlands, there exists a language gap between academic theoretical practice (as it is studied in the literary theory departments) and literary practice (which, academically, gets studied in specialized departments of Dutch literature). The Dichtersalfabet can be seen as Mettes’s attempt to close this gap. It is also an attempt to bridge the divide between theory and practice, in which he could apply his theoretical knowledge in a very unorthodox and unacademic critical mode that moreover could reach far beyond the domain of conventional criticism. Mettes’s goal was to trace a diagonal through Dutch poetic culture, to “strangle” what he perceived to be its dominant oppressive traditions of agreeable irrelevance, in order to see whatever might be able to survive his critical assaults. But he could only do so by means of a very serious engagement with poetry itself. To this end, he would go systematically through the poetry bookshelf of the Verwijs bookshop (part of a mainstream chain of booksellers) in The Hague, buying one publication per blog item, starting from A and working his way through the alphabet, reading whatever he might encounter that way in the restaurant of the HEMA store (another big commercial chain in the country). He would subsequently write down his reading experiences, refraining however from trying to write a nuanced book review. Rather, he would write about anything that caught his attention and sparked his critical interest. This way of working would yield vast, at times somewhat rambling, dense, lively, and generally brilliant essays, in which he held no punches. He never hesitated to pull out his entire arsenal of concepts from the international theory traditions, while never degenerating into mere academic exercise and pointless intertextualities. The attempt was rather to live the poetry that he read, and to engage it with the full range of political, academic, cultural, and personal references that he had at his disposal—all that composed the individual named Jeroen Mettes as a reader. Often what he wrote would not be according to the standards of what we usually think of as a critical review of a book of poetry. Sometimes he would even be a little sloppy in his judgments of poets or representations of the books he read, for example by basing an entire essay on the blurb of a book rather than its poetry content. But what he did was always brilliant writing nonetheless—virtuoso riffs on poetic fragments randomly found within capitalist society, exposing an incisive and insistent poetical sensibility. Mettes read poetry for political reasons, to see whether poetry could offer him a way to deal with a political world he detested. The right-wing horrors of the Bush years, the Iraq war, and the turn of Dutch public opinion towards ever more conservative, narrow-minded, and xenophobic views alongside a complete failure of the political left to present any credible alternative, were weighing heavily on the times in which Mettes reported on his reading. Poetry was to measure this world, diagram it, to lay bare its inconsistencies and faults, to indicate where lines of flight might be found. Amid the ruins of a world wrecked by imperialist policies, corporate capitalism, and doctrinal neoliberalism it would have to show the possibility of a new community. And it was, through its rhythmical workings, to release the reading subject from his confinement to ideologically conditioned individuality and lead him into the immanent paradise of reading. The stakes were high. Much higher than anything Dutch poetry had seen for many years. Mettes’s blog was widely read from the start. His posts sparked lively debates. Some of these subsequently led to the publication of extensive essays on a few key poets in some literary journals, particularly Parmentier and the Flemish journal yang , for which Mettes would become a member of the editorial board, a few months after starting the Dichtersalfabet . This could have been the start of a brilliant career, but this was not to be. The initial manic energy that fueled the blog gradually subsided. The Alfabet was updated less and less regularly. Mettes sometimes just disappeared for many weeks, then suddenly returning with a brilliant essay. Until, on September 21, 2006, he posted his final blogpost, consisting of no text whatsoever. That night I learned from his mentor at Leiden University that he had committed suicide. Mettes and I had had some fruitful exchanges on poetry, rhythm, music, and form, mostly on the blogs, but also by email. Three weeks before his death was the last time I heard from him: a very sudden, uncharacteristically curt note saying “My old new sentence epic.” Attached to that message I found a DOC-file of a work so major that I felt intimidated. This was N30 , a text he had been working on for over five years. After his death, it took me a long time before I dared to read it in its entirety. In the meantime, the work of preparing the manuscript for publication was entrusted by his relatives to his colleagues at yang magazine. It took them a few years to brush up the text and to edit the Dichtersalfabet -blog (which, apart from the Alphabet project itself, incorporated many other fragments of political, polemical, and theoretical writing) into book form along with the essays. The result of this labor was finally published in 2011 as a two-book set, and Mettes burst onto the Dutch poetry scene for the second time. The work was widely reviewed, on blogs, in journals, magazines, and newspapers. Many critics who had not followed the blogs in 2005 showed themselves surprised, baffled even, by the intensity of Mettes’s critical writing. But for those who had read the blog, the main surprise was in the poetry. During Mettes’s lifetime, some of his poems had already been published in Parmentier . Although these were strong texts by themselves, in no way did they prepare readers for N30 . Nothing like it had been written in Dutch before. Instead, N30 explicitly follows the American tradition of Language Writing, directly referencing Ron Silliman and his concept of The New Sentence. However, it would seem that much of the poetical thinking around his use of this technique puts him closer to a writer such as Bruce Andrews. For Mettes, using non sequiturs as a unit of poetic construction was not only a way of reinventing formal textual construction, but it was another way of finding the fault lines in the social fabric. From the perspective of the Language tradition, one may put N30 somewhere between Silliman and Andrews. N30 shares an autobiographical element with Silliman’s New Sentence projects, and as in Andrews, there is a concern for mapping out social totality within text—what Mettes refers to as a “textual world civil war.” Again this shows a formal textual strategy for allowing the person “Jeroen Mettes” to be absorbed by the world, which here appears as a whirlwind of demotic and demonic chatter, full of violence, humor, intensity, beauty, disgust, sex, commerce, and strife. Influenced as it may by American precursors, Mettes’s tone and form end up quite different from his American counterparts, consistently referencing a world that is Dutch, all too Dutch, taking on the oppressive orderliness of Dutch society with its endemic penchant for consensus by introducing chaos into its daily life and laying bare its implicit aggressions. The work’s 31 chapters each have a different feel and rhythmical outline, but none of them follow a predetermined pattern. Rather, Mettes would consistently edit and reedit the text, randomly rewriting parts of it, as he explains in his poetical creed Politieke Poëzie (Political Poetry). N30 – referring to the 1999 antiglobalist protest in Seattle – was to be the first text of a trilogy. The work itself was written “in the mode of the present.” A second text was to be written in the mode of the future, and a third one, in the mode of the past, was going to be an epic poem about the Paris Commune, and to form an alternative poetic constitution for the European project. I still deeply regret that Jeroen Mettes never got to complete those projects, just as I would be very keen on knowing what he might have had to say about more recent political developments. Instead, in 2006, he remained stuck in the horrors of the present, that ended up consuming him completely. He left Dutch literature with some of its most piercing criticism and its most profoundly moving, exciting and powerful poetry. Excerpts from N30 Translated by Vincent W.J. van Gerven Oei from Jeroen Mettes. "N30." In N30+ . Amsterdam: De wereldbibliotheek, 2011. Published with permission of Uitgeverij Wereldbibliotheek, Amsterdam. Chapter 1 1999. A day is a space too. And another man, who had chained himself, had his ribs crushed, and a motor has driven over somebody’s legs. Dutch health care system spends ±145 million guilders per year on worriers. A spiderweb vibrates as I pass by. Randstad renovating. She slaps her bag against her ass: “Hurry up!” OPINION IS TRUE FRIENDSHIP Your skin. It doesn’t express anything. “But the use of the sword, that’s what I learned, and you’ll need nothing more for the moment.” Just try to interrogate a guy like that. Gullit in Sierra Leone. Codes silently lying all around. But that’s simply what belongs to “that it’s just allowed”: that sigh of “world” (a word expressing that the trees are now standing along the water like black men with white bags in their hair); that’s nothing else right? And you see how everything has to move, and first of all what cannot do so. Without Elysium and without savings, barbarians lashing out, horny for an enemy, staring across the water, staring into the air—staring to get out of it. “You’ve never showed me more than the mall,” she said. All those “dreams” in the end—and now? It was lying on the stairway, so I picked it up and took it upstairs. Chapter 3 “You know what?” Telecommunication. For love… I don’t really like that cheap cultural pessimism, but… The holy city is on pilgrimage in the earthly bodies of the faithful until the time of the heavenly kingdom has come. The end of an exhausting autumn day behind the computer, my eyes filled with tears of fatigue. KITCHEN / INSTALLATION / SPECIALIST. Network integration. In the sun, stretched out on a sheet. (…) I don’t believe what I’m reading, because I want to believe something else. An illusion? Suits me. There’s a variety of shapes and tastes… “So what?” you may think. 102 dalmatians can’t be wrong. But I want more, dear… A feel good movie. I’m smashing the burned body. So what? We continue to save the European civilization. What’s there to win? Plato with poets = Stalin without gulag? Ball against the crossbar. No wonder. She comes straight to her point. She’s standing in the kitchen eating an apple. (…) The godless Napoleon had used her as a stable and wanted to have her taken down. “Our” Rutger Hauer. Ready or not here I come. Psst… are you also wearing a string? Nobody understands our desire. Cliffs breaking the waves and shattering the sunset. I used to be a real romantic (as a poet). A typical fantasy used to be the one in which I brutally raped mother and daughter Seaver from the sitcom Growing Pains . Nevertheless you only contain bad words. Eyelashes. Automatic or manual? That your skin always in the afternoon. Integration. The air is empty. Too bad! Hand in hand on their lonely way. Alaska! Chapter 12 May 5, 2001 [10:00-10:30] A dust cloud on a hill. Globe. Indian (British) (tie) / pope. Damascus. Rape. We’re carrying the ayatollah’s portrait through the streets. At the moment the girl is mostly suede jacket with white ribbons on her sleeves. A small explosion flares up/impact. Camouflage. Close up. We’re analyzing the situation. He’s dead right? Dead dead. Dead. Everything without, these, and only with the body. Indices signal death. Dollar bills are printed in factories. Holes. Light patch. Globe in a box. Microphone. What’s the situation? Grey impact on a green hill (field?). The water is blue. He has no lips. Interns on the background with skirts that are too long. This is an example of a sonnet. An Islamic woman pushes against the door of an electronics shop. Arrows (percentages (prices)). Is this what awaits the American? Touch screen interface. The word, an island, can only be a sign in that situation. We pull up a chair, join in on the fun. On the shelves only books about computers. One glance in the distance is enough to lighten up a luna park in the distance. She’s really desperate, especially when she laughs. Click. Ah. Next. And now it’s raining, but that’s ok. Yellow stains sliding over the south. Shallow caves light: clothes, boots, electrical equipment. 45. 22:10. Nothing gives you the right to eat more than people starving to death. The Hague. Slam dunk. Traffic light. Two H’s, one L (standing for the L (little prick)). We’re happy to say something. Clouds, small suns, temperatures, cities. The truth is never an excuse. Yellow. Yellow. Green. Yellow. Yellow. Yellow. Yellow. Green. Green. Yellow. Will you email me? Skeleton: “No.” Ex-nerds in brand-new and brightly red sport cars. $$$. I love. Shihab. Hooves in the sand. Skinny senior with over-sized sunglasses; old jockey (cap, trophy) smiling in slow motion. And there I am again, flashback, crying with my head in between my hands. Sometimes I’ve got the feeling that cannibals. Eyes: blue. Cancer. Why would I wait until tomorrow? Golden beams protruding from the lifted/lit earth. May 5, 2001 [11:30-12:45] You’ll remember this for the rest of your life. Graphs, diagrams. Bu$ine$$. Blue shirt, white collar, no neck (porn star). A name lights up. I’m hysteric. Will you join us? Letters falling in their words. Fingers set up a tent and start to dance. Young entrepreneurs from poor neighborhoods (read: black) guided by Microsoft. Kinda makes me happy, that sort of kitsch. A sense of exhaustion/impotence to see anything but the present. (…) Wouldn’t you like to? Orange explosion in an industrial zone. YOU’RE DOING THIS FOR AMNESTY INTERNATIONAL. Would you. A familiar face. Clouds and blossom. Sunflowers. Supermodels. Mountainous area in a rectangle: shades of brown, from dark to beige, more green toward the south. Tents and next to them (it’s all a blur) people. Plane. Stadium. Geometrical block of people. No, I ain’t crying. I don’t speak no more. I just want. Quote + photo. (Positive:) screaming crowd. Three-piece suit, seen from the back, before entering the arena. On the back: “Daddy abused me.” Oh, bummer. State of emergency has been declared and everyone has to cooperate. She’s cut her wrists. What we do know (…) is that there’s never been a unique word, an imperative name, nor will there ever be. [Click here for work that suits you.] Barefooted children are watching it (coherent pieces revelation of what’s lying below). Who knows how she’s changed during those two years. “Everything used to be better” + sigh. And here we are. An empty field of parquet. A city lying behind it. Explosion. Blue. A rain drop falling in my coffee. May 5, 2001 [14:30-15:30] A young Arafat on video speaking with raised finger. “I’m calling from my convertible.” Names on walls, victims, numbers… Tourists. Yellow. Yellow. “Your own child! Really, what kind of human are you?” I don’t want to hear it no more. A woman jumping out of the water in a yellow bikini against a background of fireworks and the Cheops pyramid. Thy sorrow shall become good fortune, thy complaints laudation. All planets will float and wander. Wo die Welt zum Bild wird, kommt das System (…) zur Herrschaft. It is something, but is it? May 5, 2001 [18:30-19:00] Iris. Leaves. NASDAQ. Open / and white and. For the one who’s doing nothing, just waiting. (…) NO DEFEAT is made entirely up of defeat -- since / the world it opens is always a place / formerly / unsuspected. October 2002. “Jeroen, I’m leaving for the cemetery, byeeee.” The rise of the middle class. My entire oeuvre is an ode to the. My entire head is a fight against the. God always demands what you cannot sacrifice. You may take that the easy way, but… “The state hasn’t made us, but we make the state” (Hitler). A stork exits the elevator. Skeletons of. Moscow. Helsinki. Palermo. Paris. Chapter 30 Like your paradises: nothing. United Desire, as only remaining superpower. And even though the sea is now calmer and the wind is blowing pleasantly in my face… Heart! Who determines whether a tradition is “alive”? The yellow leaf or the white branch? Mars. This sentence is a typical example. Most Dutch people are happy. No consolation. When I see a girl sitting at a table with a book, a notepad, a pen, a bottle of mineral water, her hand writing in the light—then I consider that one thing. “Presents,” “poetry,” “classics.” We are what we cannot make from ourselves. “Left”: mendicant orders, missionaries. Saint-Just: “A republic is founded on the destruction of its enemies.” She crosses the street with a banana peel between her fingers. (…) We chose our own wardens, torturers, it was us who called all this insanity upon ourselves, we created this nightmare… But “no”? Girl (just like a beach ball) talking rapid Spanish (Portuguese?) in a mobile phone. Do I have a chance now that her boyfriend is getting bold? CLIO, horny bitch. What else do you want? An old woman, between the doors of the C1000, is suddenly unable to go on; her husband stretches out his hand, speaking a few encouraging words. Selection from. Der Führer schenkt den Jüden ein Stadt. How can it reach us if we haven’t been already reached somehow? It doesn’t “speak.” No problem. Each word she uses is a small miracle, as if she doesn’t belong to it, to language, but wanders around with a pocket light looking for the exit; she’s never desperate (maybe a little nervous), lighting up heavy words from the inside. But indeed, we’re free. But the predicate is not an attribute, but an event, and the subject is not a subject, but a shell. That’s why also samurai, knights, and warriors raised the blossom as emblem: they knew how to die. Locked up in a baby carriage with a McDonald’s balloon. Blue helicopter, the blue sky. Whether you want to refer? The point is. How / Motherfucker can I sing a sad song / When I remember Zion? You’ll feel so miserable and worthless that you think: “If only I were dead!,” or: “Just put an end to it!” “So you’re an economist?” Her card—two little birds building a nest, her handwriting shaking—is still on the mantelpiece. Guevara: “No, a communist.” A straw fire, such was our life: rapidly it flared up, rapidly it passed. I’m fleeing, coming from nowhere. (…) Eazy-E drinking coffee with the American president. If I’d scream, would that be an event? Drown it: the cleaner it will rise up from the depths. No! The night, so fast… As if there’s something opened up in that face. Come on, we may not curse life. He shows me his methadone: “If you drink that all at once, you’ll die instantly.” The last one dictates how we should behave to deserve happiness. One shine / above the earth. “I want to go to Bosnia,” I said bluntly. I don’t even know the name of the current mayor. Let’s despise our success! “There is no future; this is the future. Hope is a weakness that we've overcome. We have found happiness!” Sun. Sushi. Volvo. I feel like a bomb about to explode at any moment. Makes a difference for the reconstruction right? The decor moves forward. Daughter of Nereus, you nymphs of the sea, and you Thetis, you should have kept his tired head above the waves! Alas! This sentence has been written wearing a green cap. I receive my orders from the future. A frog jumps into it. Her husband has turned the Intifada, which he follows daily on CCN, into his hobby, “to forget that he doesn’t have his driver’s license yet." Suddenly the sun slides over the crosswalk. Her (his?) foot is playing with the slipper under the table. Is this how I’m writing this book now? I’m not a fellow man. I hate you and I want to hurt you. These are my people. Their screaming doesn’t rise above the constantly wailing sirens which we've learned to ignore. My whole body became warm and suddenly started to tremble. Unfortunate is he who is standing on the threshold of the most beautiful time, but awaits a better one. Arafat’s “removal” is contrary to American interests. Jeep drives into boy. What you can do alone, you should do alone. A food gift from the people of the United States of America. Two seagulls. [...]. (shrink)

Dynamic Topological Logic ( ) is a modal logic which combines spatial and temporal modalities for reasoning about dynamic topological systems , which are pairs consisting of a topological space X and a continuous function f : X → X . The function f is seen as a change in one unit of time; within one can model the long-term behavior of such systems as f is iterated. One class of dynamic topological systems where the long-term behavior of f is (...) particularly interesting is that of minimal systems ; these are dynamic topological systems which admit no proper, closed, f -invariant subsystems. In such systems the orbit of every point is dense, which within translates into a non-trivial interaction between spatial and temporal modalities. This interaction, however, turns out to make the logic simpler, and while s in general tend to be undecidable, interpreted over minimal systems we obtain decidability, although not in primitive recursive time; this is the main result that we prove in this paper. We also show that interpreted over minimal systems is incomplete for interpretations on relational Kripke frames and hence does not have the finite model property; however it does have a finite non-deterministic quasimodel property. Finally, we give a set of formulas of which characterizes the class of minimal systems within the class of dynamic topological systems, although we do not offer a full axiomatization for the logic. (shrink)

Given two (positive) equivalence relations ∼ 1 , ∼ 2 on the set ω of natural numbers, we say that ∼ 1 is m-reducible to ∼ 2 if there exists a total recursive function h such that for every x, y ∈ ω, we have $x \sim_1 y \operatorname{iff} hx \sim_2 hy$ . We prove that the equivalence relation induced in ω by a positive precomplete numeration is complete with respect to this reducibility (and, moreover, a "uniformity property" holds). This (...) result allows us to state a classification theorem for positive equivalence relations (Theorem 2). We show that there exist nonisomorphic positive equivalence relations which are complete with respect to the above reducibility; in particular, we discuss the provable equivalence of a strong enough theory: this relation is complete with respect to reducibility but it does not correspond to a precomplete numeration. From this fact we deduce that an equivalence relation on ω can be strongly represented by a formula (see Definition 8) iff it is positive. At last, we interpret the situation from a topological point of view. Among other things, we generalize a result of Visser by showing that the topological space corresponding to a partition in e.i. sets is irreducible and we prove that the set of equivalence classes of true sentences is dense in the Lindenbaum algebra of the theory. (shrink)

That surely includes the timing of the assault: shortly before noon, when children were returning from school and crowds were milling in the streets of densely populated Gaza City. It took only a few minutes to kill over 200 people and wound 700, an auspicious opening to the mass slaughter of defenseless civilians trapped in a tiny cage with nowhere to flee.1..

Ask any clinical ethics consultant, and they can tell you about their transformative cases. Some stick with us because all roads led nowhere. Cassandra Lee had a history of pulling out lines and tubes and a distaste of warming blankets. Her admission marked her thirtieth over the past year. Many of the challenges facing the hospital caring for her were not unique: significant psychiatric issues, prolonged nonadherence to medical advice, and end‐of‐life decision‐making combined to create an ethically dense (...) and vexing situation. Ms. Lee, like so many patients, was suffering because of system failures. (shrink)

In this paper we prove that the preordering $\lesssim $ of provable implication over any recursively enumerable theory $T$ containing a modicum of arithmetic is uniformly dense. This means that we can find a recursive extensional density function $F$ for $\lesssim $. A recursive function $F$ is a density function if it computes, for $A$ and $B$ with $A\lnsim B$, an element $C$ such that $A\lnsim C\lnsim B$. The function is extensional if it preserves $T$-provable equivalence. Secondly, we (...) prove a general result that implies that, for extensions of elementary arithmetic, the ordering $\lesssim $ restricted to $\Sigma_{n}$-sentences is uniformly dense. In the last section we provide historical notes and background material. (shrink)

Cooper proved in [S.B. Cooper, Strong minimal covers for recursively enumerable degrees, Math. Logic Quart. 42 191–196] the existence of a c.e. degree with a strong minimal cover . So is the greastest c.e. degree below . Cooper and Yi pointed out in [S.B. Cooper, X. Yi, Isolated d.r.e. degrees, University of Leeds, Dept. of Pure Math., 1995. Preprint] that this strongly minimal cover cannot be d.c.e., and meanwhile, they proposed the notion of isolated degrees: a d.c.e. degree is (...) isolated by a c.e. degree if is the greatest c.e. degree below , and we also say that isolates . In [G. Wu, Bi-isolation in the d.c.e. degrees, J. Symbolic Logic 69 409–420], Wu extended Cooper–Yi’s notion and proved that there are intervals of d.c.e. degrees containing exactly one c.e. degree . Following Cooper and Yi’s notion, is called a bi-isolating degree. The bi-isolating degrees are dense in the high c.e. degrees. Arslanov asked whether the bi-isolating degrees occur in every jump class. In this paper, we prove that there are low bi-isolating degrees, providing a partial solution to Arslanov’s question. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Reviewed by:A Report from the Front Lines: Conversations on Public Theology. A Festschrift in Honor of Robert Benne, and: Explorations in Christian Theology and Ethics: Essays in Conversation with Paul L. LehmannJeffrey P. GreenmanA Report from the Front Lines: Conversations on Public Theology. A Festschrift in Honor of Robert Benne Edited by Michael Shahan Grand Rapids, Mich.: Eerdmans, 2009. 184 pp. $30.00.Explorations in Christian Theology and Ethics: Essays in (...) Conversation with Paul L. Lehmann Edited by Philip G. Ziegler and Michelle J. Bartel Farnham, Surrey, UK: Ashgate, 2009. 206 pp. $99.95.The volumes reviewed here each recognize an important thinker in Christian social ethics in America: Robert Benne, emeritus professor of religion at Roanoke College, a Lutheran social ethicist; and Paul L. Lehmann (1906–94), a Presbyterian who was an influential teacher associated with Princeton Theological Seminary, Harvard University Divinity School, and Union Theological Seminary in New York.The first volume honors Benne’s seventieth birthday. His major writings include The Ethic of Democratic Capitalism: A Moral Reassessment (1981), Ordinary Saints: An Introduction to the Christian Life (1988), The Paradoxical Vision: A Public Theology for the Twenty-First Century (1995), Quality with Soul: How Six Premier Colleges and Universities Keep Faith with Their Religious Traditions (2001), and most recently, Good and Bad Ways to Think about Religion and Politics (2010). Since Benne is known for his traditionalist moral views, some unmistakably conservative voices, including a number of prominent Lutherans and neoconservative political thinkers, are represented in this book. The broad theme is public theology, working from Benne’s definition of public theology as “the engagement of a living religious tradition with its public environment—the economic, political, and cultural spheres of our common life.”The book has three parts. The first section, “The Imperative of a Public Theology,” includes essays by editor Michael Shahan, Carl Braaten, Jean Bethke Elshtain, and Richard John Neuhaus. Shahan’s essay provides a helpful exposition of Benne’s intellectual trajectory. Braaten offers a defense of the historic, bodily resurrection of Jesus as the “crux of Christianity’s case.” Elshtain takes [End Page 206] up C. S. Lewis’s concerns in his Abolition of Man (1944) as she diagnoses the “cultural disorder” reflected in current debates about euthanasia and abortion. Neuhaus’s wistful essay looks back over his efforts in the public square, stating that he and Benne have shared a common concern: “A renewal of Christian confidence in providing a morally informed philosophy for a more just and virtuous society in the tradition of liberal democracy” (47). Taken together, these four chapters sketch the assumed intellectual and cultural landscape that sets the context for the volume as a whole.The second section, “The Lutheran Necessity in Public Theology,” begins with a largely autobiographical essay by James Nuechterlein about his journey in Lutheranism and the value of its theological distinctives, especially the famous simul. Next is Gilbert Meilaender’s account (exploring an insight from Kierkegaard) of the place for a Lutheran “corrective” within the wider normative tradition, then Mark Noll’s chapter that underscores the value of robust Lutheran social thinking against the backdrop of the more revivalist and pietist tendencies of Protestant evangelicalism.The final section, “Contested Issues in Public Theology,” includes chapters by Paul Hinlicky, Ronald Thiemann, Gerald McDermott, Donald Schmeltekopf and Michael Beaty, and Joseph Swanson. The chapters by Hinlicky on Luther’s relation to liberal political theory, and by Thiemann on the idea of the public theologian’s prophetic role as “connected critic,” are the most densely argued material in the book. These two essays will probably be of the most interest for scholars in theological ethics. The chapter by McDermott deals with Lutheran church-related colleges. A coauthored essay by Schmeltekopf and Beaty champions the vocation of Christian university education. Swanson situates Benne’s economic writings within neo-conservative thought.The book takes up some of Benne’s favorite themes and interest areas, but only rarely do the authors engage Benne’s own thought. Virtually nowhere do they prod Benne to become clearer, to strengthen his arguments, or to modify his conclusions. I would have preferred a deeper engagement with Benne’s ideas; in several... (shrink)