A derived algorithm for evaluating ε-expressions over abstract sets

  • Authors:
  • Eugenio G. Omodeo;Franco Parlamento;Alberto Policriti

  • Affiliations:
  • Università di Roma La Sapienza. Italy;Università di Udine, Italy;Università di Udine and Courant Institute of Mathematical Sciences, Italy

  • Venue:
  • Journal of Symbolic Computation - Special issue on automatic programming
  • Year:
  • 1993

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Abstract

Four weak theories of pure sets are axiomatically characterized. A decision method is given for checking sentences of the form @?"y"1...@?"y"n@?"x"p, where n varies over natural numbers and p over unquantified matrices, for provability in each theory. Dually, the method can be used to check @?"y"1...@?"y"n@?"x"@?"p for satisfiability. The completeness proof is fully constructive: this means that given a satisfiable constraint of the form @?"y"1...@?"y"n@?"x"@?"p, a computable model of the axioms which also fulfills the constraint can be synthesized. In this sense, we have a way of automatically generating a concrete representation of the abstract data-type ''set'' under varying axioms. The problem is also addressed of how to determine @? x p; i.e., how to find a @z fulfilling p(@x"1,...,@x"n,@z) in a computable model M of one of our theories, as a function of input M-sets @x"1,...,@x"n. A partial solution to this problem is supplied, which works when @?"y"1...@?"y"n@?"x"p is a theorem and M meets a suitable condition which happens to be satisfied by those models that are produced by our automatic synthesis algorithm. A stronger condition on M is also characterized that makes @? x p computable in all cases (at worst through a blind search method). Examples showing the expressive power of the @?*@?-constraints and the usefulness of @?-expressions in set computations are included. Envisaged extensions of the proposed methods to axiomatic set theories antithetic to the classical ones are briefly hinted at.