On Equality Up-to Constraints over Finite Trees, Context Unification, and One-Step Rewriting
نویسندگان
چکیده
We introduce equality up-to constraints over nite trees and investigate their expressiveness. Equality up-to constraints subsume equality constraints, subtree constraints, and one-step rewriting constraints. We establish a close correspondence between equality up-to constraints over nite trees and context uniication. Context uniication subsumes string uniication and is subsumed by linear second-order uni-cation. We obtain the following three new results. The satissability problem of equality up-to constraints is equivalent to context uniica-tion, which is an open problem. The positive existential fragment of the theory of one-step rewriting is decidable. The 9 8 9 fragment of the theory of context uniication is undecidable.
منابع مشابه
On Equality Up-to Constraints over Finite Trees, Context Uni cation, and One-Step Rewriting
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