for every variable "p". A complete set of unifiers of a formula "A" is a set "S" of "L"-unifiers of "A" such that every "L"-unifier of "A" is less general than some unifier from "S". A most general unifier (mgu) of "A" is a unifier σ such that {σ} is a complete set of unifiers of "A". It follows that if "S" is a complete set of unifiers of "A", then a rule "A"/"B" is "L"-admissible if and only if every σ in "S" is an "L"-unifier of "B". Thus we can characterize admissible rules if we can find well-behaved complete sets of unifiers.