(* Title: Subst/unifier.thy
Author: Martin Coen, Cambridge University Computer Laboratory
Copyright 1993 University of Cambridge
Definition of most general unifier
*)
Unifier = Subst +
consts
Unifier :: "[('a*('a uterm))list,'a uterm,'a uterm] => bool"
">>" :: "[('a*('a uterm))list,('a*('a uterm))list] => bool" (infixr 52)
MGUnifier :: "[('a*('a uterm))list,'a uterm,'a uterm] => bool"
Idem :: "('a*('a uterm))list => bool"
rules (*Definitions*)
Unifier_def "Unifier s t u == t <| s = u <| s"
MoreGeneral_def "r >> s == ? q. s =s= r <> q"
MGUnifier_def "MGUnifier s t u == Unifier s t u &
(!r. Unifier r t u --> s >> r)"
Idem_def "Idem(s) == s <> s =s= s"
end