In this paper we introduce a collection of isols having some interesting properties. Imagine a collection W of regressive isols with the following features: u, v ϵ W implies that u ⩽ v or v ⩽ u, u ⩽ v and v ϵ W imply u ϵ W, W contains ℕ = {0,1,2,…} and some infinite isols, and u eϵ W, u infinite, and u + v regressive imply u + v ϵ W. That such a collection W exists is (...) proved in our paper. It has many nice features. It also satisfies u, v ϵ W, u ⩽ v and u infinite imply v ⩽ g for some recursive combinatorial function g, and each u ϵ W is hereditarily odd-even and is hereditarily recursively strongly torre. The collection W that we obtain may be characterized in terms of a semiring of isols D introduced by J. C. E. Dekker in [5]. We will show that W = D, where c is an infinite regressive isol that is called completely torre. (shrink)

We give a correction to the paper [1] mentioned in the title.

In this paper we present a contribution to a classical result of E. Ellentuck in the theory of regressive isols. E. Ellentuck introduced the concept of a hyper-torre isol, established their existence for regressive isols, and then proved that associated with these isols a special kind of semi-ring of isols is a model of the true universal-recursive statements of arithmetic. This result took on an added significance when it was later shown that for regressive isols, the property of being hyper-torre (...) is equivalent to being hereditarily odd-even. In this paper we present a simplification to the original proof for establishing that equivalence. (shrink)

In this paper we present a collection of results related to the comparability of summands property of regressive isols. We show that if an infinite regressive isol has comparability of summands, then every predecessor of the isol has a weak comparability of summands property. Recently R. Downey proved that there exist regressive isols that are both hyper-torre and cosimple. There is a surprisingly close connection between non-recursive recursively enumerable sets and particular retraceable sets and regressive isols. We apply the theorem (...) of Downey to show that among the regressive isols that are related to recursively enumerable sets there are some with a new property. (shrink)

In [14] J. Hirschfeld established the close connection of models of the true AE sentences of Peano Arithmetic and homomorphic images of the semiring of recursive functions. This fragment of Arithmetic includes most of the familiar results of classical number theory. There are two nice ways that such models appear in the isols. One way was introduced by A. Nerode in [20] and is referred to in the literature as Nerode Semirings. The other way is called a tame model. It (...) is very similar to a Nerode Semiring and was introduced in [6]. The model theoretic properties of Nerode Semirings and tame models have been widely studied by T. G. McLaughlin ([16], [17], and [18]). In this paper we introduce a new variety of tame model called a torre model. It has as a generator an infinite regressive isol with a nice structural property relative to recursively enumerable sets and their extensions to the isols. What is then obtained is a nonstandard model in the isols of the Π0 2 fragment of Peano Arithmetic with the following property: Let T be a torre model. Let f be any recursive function, and let fΛ be its extension to the isols. If there is an isol A with fΛ(A)∈ T, then there is also an isol B∈ T with fΛ(B) = fΛ(A). (shrink)