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dc.contributor.authorKozen, Dexter
dc.date.accessioned2010-05-19T16:04:59Z
dc.date.available2010-05-19T16:04:59Z
dc.date.issued2010-05-19T16:04:59Z
dc.identifier.urihttps://hdl.handle.net/1813/14998
dc.description.abstractIn this note we consider the following decision problems. Let S be a fixed first-order signature. (i) Given a first-order theory or ground theory T over S of Turing degree A, a program scheme p over S, and input values specified by ground terms t1,...,tn, does p halt on input t1,...,tn in all models of T? (ii) Given a first-order theory or ground theory T over S of Turing degree A and two program schemes p and q over S, are p and q equivalent in all models of T? When T is empty, these two problems are the classical halting and equivalence problems for program schemes, respectively. We show that problem (i) is Sigma^A_1-complete and problem (ii) is Pi^A_2-complete. Both problems remain hard for their respective complexity classes even if S is restricted to contain only a single constant, a single unary function symbol, and a single monadic predicate. It follows from (ii) that there can exist no relatively complete deductive system for scheme equivalence over models of theories of any Turing degree.en_US
dc.description.sponsorshipNSF CCF-0635028en_US
dc.language.isoen_USen_US
dc.subjectdynamic model theoryen_US
dc.subjectprogram schemeen_US
dc.subjectscheme equivalenceen_US
dc.titleHalting and Equivalence of Program Schemes in Models of Arbitrary Theoriesen_US
dc.typetechnical reporten_US


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