Syntactic, Commutative and Associative Anti-Unification
Anti-Unification, Equational Theory, Associativity, Commutativity.
This dissertation presents a detailed study of the Anti-Unification Problem, originally investigated by Plotkin and Ploppestone in the early 70's. This problem consists of finding a term that maintains the greatest common structure between two other given terms. That is, given s and t, the problem is to find a third term r, with a notion (to be defined) of maximality, such that there are substitutions σ 1 and σ 2 such that rσ 1 = s and rσ 2 = t. Such a
term r is called the least general generalizer of s and t. In this work we will investigate the Syntactic Anti-Unification Problem, that is when we consider the syntactic equality between the terms; and also the Anti-Unification Problems
modulo Commutativity (C) and Associativity (A), that is, when the anti-unification problem considers the equalities modulo C and modulo A, respectively. In all cases, we present an algorithm for solving the problem in addition to its termination, soundness, and completeness properties. From the properties of each algorithm, we will then present the properties of the sets of solutions for each problem.