Syntactic Uni cation Problems under Constrained Substitutions
نویسندگان
چکیده
Some kind of practical problems such as security veri cation of cryptographic protocols can be described as a problem to accomplish a given purpose by using limited operations and limited materials only. To model such problems in a natural way, uni cation problems under constrained substitutions have been proposed. This paper is a collection of results on the decidability and the computational complexity of a syntactic uni cation problem under constrained substitutions. A number of decidable, undecidable, tractable and intractable results of the problem are presented. Since a uni cation problem under constrained substitutions can be regarded as an order-sorted uni cation problem with term declarations such that the number of sorts is only one, the results presented in this paper also indicate how the intractability of order-sorted uni cation problems is reduced by restricting the number of sorts to one. key words: uni cation problem, decidability, computational complexity, order-sorted signature, tree automata
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