A relaxed condition for avoiding the occur-check

We generalize the notion of “not subject to occur-check” (NSTO), on which most known results on avoiding the occur-check in logic programming are based. NSTO means that unification is performed only on such pairs of atoms for which the occur-check never succeeds in any run of a nondeterministic unif...

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Veröffentlicht in:Theoretical computer science Jg. 975; S. 114107
1. Verfasser: Drabent, Włodzimierz
Format: Journal Article
Sprache:Englisch
Veröffentlicht: Elsevier B.V 09.10.2023
Schlagworte:
Delays/coroutining
Logic programming
Modes
Occur-check
Selection rule
SLD-resolution
Unification
Modes
Logic programming
Unification
Occur-check
Selection rule
Delays/coroutining
SLD-resolution
ISSN:0304-3975
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Zusammenfassung:We generalize the notion of “not subject to occur-check” (NSTO), on which most known results on avoiding the occur-check in logic programming are based. NSTO means that unification is performed only on such pairs of atoms for which the occur-check never succeeds in any run of a nondeterministic unification algorithm. Here we show that “any run” can be weakened to “some run”. We present some related sufficient conditions under which the occur-check may be safely omitted. We show examples for which the proposed approach provides more general results than the approaches based on well-moded and nicely moded programs (this includes cases to which the latter approaches are inapplicable). We additionally present a sufficient condition based on NSTO, working for arbitrary selection rules. •We deal with sufficient conditions for avoiding the occur-check in unification.•Such conditions have been based on a notion of “not subject to occur-check” (NSTO).•We propose a less restrictive version of NSTO.•It widens the class of cases dealt with.•Also, it leads to simpler sufficient conditions than NSTO, for some cases.
ISSN:0304-3975
DOI:10.1016/j.tcs.2023.114107