Unranked Anti-Unification with Hedge and Context Variables

In this work we study anti-unification for unranked terms and hedges, permitting context and hedge variables. Hedges are sequences of unranked terms. The anti-unification problem of two hedges s̃ and q̃ is concerned with finding their generalization, a hedge g̃ such that both s̃ and q̃ are instances of g̃ under some substitutions. Context variables are used to abstract vertical differences in the input hedges, and hedge variables are used to abstract horizontal differences. A rule based system in Huet’s style will be presented, which computes a set of generalizations of input hedges and records all the differences. The computed generalizations are least general among a certain class of generalizations.