Skeletons and Predicate Specifications

A skeleton for a functor f/n is a structure of the form f($Arg_1$,...,$Arg_n$) where each $Arg_i$ is a distinct variable. Similarly the skeleton of a term is the skeleton formed from the principal functor of the term, so that skeletons from the terms f(1,2) and f(A,B) are the same. A return skeleton is a specific application of this notion to answer returns. From it, one may discern the size of the template for a given subgoal. Finally, we assume that a predicate specification for a predicate p and arity n, represented as PredSpec below, can be given either using the notation p/n or as a skeleton, p($t_1$,...,$t_n$).