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EN
We report on an investigation aimed at identifying small fragments of set theory (typically, sublanguages of Multi-Level Syllogistic) endowed with polynomial-time satisfiability decision tests, potentially useful for automated proof verification. Leaving out of consideration the membership relator ∈ for the time being, in this paper we provide a complete taxonomy of the polynomial and the NP-complete fragments involving, besides variables intended to range over the von Neumann set-universe, the Boolean operators ∪, ∩, \, the Boolean relators ⊆, ⊈,=, ≠, and the predicates ‘• = Ø’ and ‘Disj(•, •)’, meaning ‘the argument set is empty’ and ‘the arguments are disjoint sets’, along with their opposites ‘• ≠ Ø and ‘¬Disj(•, •)’. We also examine in detail how to test for satisfiability the formulae of six sample fragments: three sample problems are shown to be NP-complete, two to admit quadratic-time decision algorithms, and one to be solvable in linear time.
2
Content available remote An Improved Set-based Reasoner for the Description Logic 𝒟ℒD4,×
EN
We present a KE-tableau-based implementation of a reasoner for a decidable fragment of (stratified) set theory expressing the description logic 𝒟ℒ〈4LQSR,×〉(D ) (𝒟 ℒD 4,×, for short). Our application solves the main TBox and ABox reasoning problems for 𝒟 ℒ D 4,×. In particular, it solves the consistency and the classification problems for 𝒟 ℒD 4,× -knowledge bases represented in set-theoretic terms, and a generalization of the Conjunctive Query Answering problem in which conjunctive queries with variables of three sorts are admitted. The reasoner, which extends and improves a previous version, is implemented in C++. It supports 𝒟 ℒ D 4,×-knowledge bases serialized in the OWL/XML format and it admits also rules expressed in SWRL (Semantic Web Rule Language).
3
Content available remote Mapping Sets and Hypersets into Numbers
EN
We introduce and prove the basic properties of encodings that generalize to non-wellfounded hereditarily finite sets the bijection defined by Ackermann in 1937 between hereditarily finite sets and natural numbers.
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