Answer Set Programming is a new paradigm based on logic programming. The main component of answer set programming is a system that finds the answer sets of logic programs. During the computation of an answer set, systems are faced with choice points where they have to select a literal and assign it a truth value. Generally, systems utilize some heuristics to choose new literals at the choice points. The heuristic used is one of the key factors for the performance of (...) the system. A new heuristic for answer set programming has been developed. This heuristic is inspired by hierarchical planning. The notion of criticality, which was introduced for generating abstraction hierarchies in hierarchical planning, is used in this heuristic. The resulting system (CSMODELS) uses this new heuristic in a static way. CSMODELS is based on the system SMODELS. The experimental results show that this new heuristic is promising for answer set programming. A comparison of search times with SMODELS demonstrate CSMODELS’ usefulness. (shrink)

Khalīfa b. Khayyāt(d. 240/854-855) was an historian- muḥaddith in the ʿAbbāsid’s period. There are references in sources to his competence in history and lineage rather than Ḥadīth. Two works of him have survived. The first one is al-Ṭabaḳāt which is about study of men and the second one is al-Taʾrīkhwhich chronologically narratesthe events in the history of Islam until 232 AH. The latter is the most significant work to be applied for the historiography of ibnKhayyāt. In this article, Khalīfa b. (...) Khayyāt’s methodology in historiography is examined. In this study, the early period of Islamic histography is handled and the subject is discussed comparatively. The main characteristics of his historiography are his adoption of a chronological style that facilitates the follow-up of the book, his knowledge for the lineage of those who died in wars and the details about the wars. Also, among the charactersitics are his application of isnād to his history book as a muḥaddith, his knowledge for the previous resources via his teachers who belong to the schools of al-Madīna and ʿIrāḳ and when required, his usage of ayah, ḥadīth and poems. These issues are dealed in the artcile with examples. Besides, a study in the West about Khalīfa b. Khayyātasserts that he was a follower of Umayyad dynasty and so this affected his historiography. In this article, this assertion is tackled by analyzing the whole book and it concludes that it is not valid because of some narrations against this assertion.SummaryKhalīfa b. Khayyāt (d. 240 / 854-55), who grew up in Basra, one of the most important centers of scholarship of the time and the meeting point of scholars, and he continued his scholarly works in this city. Since his grandfather and father are engaged in the field of Ḥadīth, Khalīfa b. Khayyāt started his scholarly adventure at an early age and he took his first education in the field of Ḥadīth.Scholars, in the early periods, continued their studies in the fields of sciences related to each other. Khalīfa b. Khayyāt’s studies are also in this kind. Although there are references in sources to his accumulation of Ḥadīth, Khalīfa b. Khayyāt ’s main area of ​​expertise is history and nasab/genealogy. The fact that his works and references to him in later sources are largely related to historical events, knowledge of the nasab/genealogy, and wafayāt (death dates of Ḥadīth scholars and narrators) reveals his considerable knowledge on these issues. Khalīfa b. Khayyāt lived in the period of ʿAbbāsid caliphs al-Maʾmūn (813-833) and al-Muʿtaṣim (833-842). This period is important because of the fact that the al-Mihna incident took place and the pressure on the Ḥadīth scholars increased. Although Khalīfa b. Khayyāt is not one of the direct opponents of Muʿtazila, his participation in a debate against them provides clues about the place where he stands. The scholarly atmosphere of Basra, enabled Khalīfa b. Khayyāt to benefit from a wide range of teacher-student network. In addition to his professors from whom he benefitted in the field of Ḥadīth, he had the opportunity to obtain the knowledge and understanding of the history of that time through his teachers who are important historians of the period in his field. Two works related to Khalīfa b. Khayyāt whose reliability is confirmed by djarh wa l tadil scholars reached to our time. One of the oldest Ṭabaḳāt works in the history of Islam is al-Ṭabaḳāt; the other one is the book, al-Taʾrīkh, which provides a new method for Islamic historiography.This study deals with the principles of the method of historiography, which can be put forward through Khalīfa b. Khayyāt 's al-Taʾrīkh. al-Taʾrīkhis important in terms of being the first example of chronological writing type in Islamic historiography and has not been subject to any independent study to date. There are two ongoing M.A. thesis about Khalīfa b. Khayyāt, however, no study has been identified that directly deals with its methodology of history. On the other hand, based on some riwāyats/narrations in al-Taʾrīkh, there is a work that claims that Khalīfa b. Khayyāt had sympathy towards Umayyads. The study named “Khalīfa b. Khayyāt’s History on the Umayyad Dynasty (660-750), prepared by Carl Wurtzel as his PhD. Dissertation, examined the life of Khalīfa, partly the historiography and the religious-political narrations in the work. On the case of Muʿāwiya’s (d. 60/680) request of the allegiance to Yazīd (d. 64/683), Wurtzel compared an event that took place between the envoy of Ibn al-Zubayr (d. 73/692) and Muʿāwiya with al-Balādhurī’s (d. 279/892-93) narrative and concluded that Khalīfa was an Umayyad sympathizer. However, Khalīfa b. Khayyāt’s exclusion of an event such as al-Mihna which was against the ʿAbbāsid and changed the course of history in his book, shouldn’t be considered as a symptom of sympathy; It would be more appropriate to accept it as a feature of history writing.At the top of Khalīfa b. Khayyāt's principles of historiography, adopting chronological method comes first. Accordingly, Khalīfa b. Khayyāt, gives a brief history about the siyar of the Prophet Muhammad at the introduction of the book. Then, by beginning from the first hijri year, he gives the important events, wars and deaths by the years. Sometimes, he refers to the people assigned by the caliphs of the period by referring to the Amîrs (Administrators) of the Hajj. He gives lists of those who died on both sides of the wars. The importance of mentioning the tribes of the deceased shows his competence in the knowledge of nasab. One of the highlights of his historiography is that he sometimes does not touch upon some of the events and situations that are considered to be turning points in Islamic history; and sometimes he does not go down into detail but just gives relevant narratives. For example, he doesn’t mention any narrations about the selection of the Caliph which perhaps the most fundamental point of separation between Ahl al-Sunnah and Shīʿa in the history of Islam.Although he gave detailed information about The Battle of The Camel (36/656) and Ṣiffīn cases (37/657), it is not possible to determine his views on this subject. In addition, he never mentioned the al-Mihna incident, which deeply influenced society and the scholarly environment during the ʿAbbāsid period. Isnād is also holds an important place in the methodology of history of Khalīfa who was a muḥaddith at the same time. In many of the narrations he used the words haddathanā and ahbaranā.In our study, the siyar section of al-Taʾrīkhwas examined in order to determine the sources of the Khalīfa’s historiography and has been seen that the works of Ibn Isḥāḳ (d. 151/768) and Ibn Hishām (d. 218/833) were the main sources of this chapter. Considering Khalīfa b. Khayyāt’s emphasize to isnād and his reach to Ibn Isḥāḳ 's work through the mediation of Bekr b. Suleiman, it can be said that he was dominant in historiography on the sources before him. Khalīfa b. Khayyāt rarely refers to Qur’anic verses and hadiths when describing events. He referred to the verses in only two places and hadiths in only five places. One of them, and perhaps the most remarkable one in the book is the Ḥadīth of the Prophet Muḥammad: “I am the guardian of whom; ‘Alī is his guardian” This narration is used in the letter of Caliph Mahdī (d. 169/785) of the ʿAbbāsid to khārijī (outer) Abd al-Salām b. Hishām who rebelled. The study is based on the principles outlined above. At the end of the study it is also considered that Khalīfa b. Khayyāt ’s works should be the subject of graduate studies which should be prepared with deep readings. (shrink)