On equality up-to constraints over finite trees, context unification, and one-step rewriting [chapter]

Joachim Niehren, Manfred Pinkal, Peter Ruhrberg
<span title="">1997</span> <i title="Springer Berlin Heidelberg"> <a target="_blank" rel="noopener" href="https://fatcat.wiki/container/2w3awgokqne6te4nvlofavy5a4" style="color: black;">Lecture Notes in Computer Science</a> </i> &nbsp;
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 uni cation. Context uni cation subsumes string uni cation and is subsumed by linear second-order unication. We obtain the following three new results. The satis ability problem of equality
more &raquo; ... o constraints is equivalent to context uni cation, 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 uni cation is undecidable.
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