diff -r bca33c49b083 -r 8408a06590a6 src/HOL/Subst/Unifier.thy
--- a/src/HOL/Subst/Unifier.thy	Mon Mar 28 16:19:56 2005 +0200
+++ b/src/HOL/Subst/Unifier.thy	Tue Mar 29 12:30:48 2005 +0200
@@ -1,12 +1,15 @@
-(*  Title:      Subst/Unifier.thy
-    ID:         $Id$
+(*  ID:         $Id$
     Author:     Martin Coen, Cambridge University Computer Laboratory
     Copyright   1993  University of Cambridge
 
-Definition of most general unifier
 *)
 
-Unifier = Subst + 
+header{*Definition of Most General Unifier*}
+
+theory Unifier
+imports Subst
+
+begin
 
 consts
 
@@ -17,9 +20,76 @@
 
 defs
 
-  Unifier_def      "Unifier s t u == t <| s = u <| s"
-  MoreGeneral_def  "r >> s == ? q. 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"
+  Unifier_def:      "Unifier s t u == t <| s = u <| s"
+  MoreGeneral_def:  "r >> s == ? q. 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"
+
+
+
+lemmas unify_defs = Unifier_def MoreGeneral_def MGUnifier_def
+
+
+subsection{*Unifiers*}
+
+lemma Unifier_Comb [iff]: "Unifier s (Comb t u) (Comb v w) = (Unifier s t v & Unifier s u w)"
+by (simp add: Unifier_def)
+
+
+lemma Cons_Unifier: "[| v ~: vars_of t; v ~: vars_of u; Unifier s t u |] ==> Unifier ((v,r)#s) t u"
+by (simp add: Unifier_def repl_invariance)
+
+
+subsection{* Most General Unifiers*}
+
+lemma mgu_sym: "MGUnifier s t u = MGUnifier s u t"
+by (simp add: unify_defs eq_commute)
+
+
+lemma MoreGen_Nil [iff]: "[] >> s"
+by (auto simp add: MoreGeneral_def)
+
+lemma MGU_iff: "MGUnifier s t u = (ALL r. Unifier r t u = s >> r)"
+apply (unfold unify_defs)
+apply (auto intro: ssubst_subst2 subst_comp_Nil)
+done
+
+lemma MGUnifier_Var: "~ Var v <: t ==> MGUnifier [(v,t)] (Var v) t"
+apply (simp (no_asm) add: MGU_iff Unifier_def MoreGeneral_def del: subst_Var)
+apply safe
+apply (rule exI)
+apply (erule subst, rule Cons_trivial [THEN subst_sym])
+apply (erule ssubst_subst2)
+apply (simp (no_asm_simp) add: Var_not_occs)
+done
+
+declare MGUnifier_Var [intro!]
+
+
+subsection{*Idempotence*}
+
+lemma Idem_Nil [iff]: "Idem([])"
+by (simp add: Idem_def)
+
+lemma Idem_iff: "Idem(s) = (sdom(s) Int srange(s) = {})"
+by (simp add: Idem_def subst_eq_iff invariance dom_range_disjoint)
+
+lemma Var_Idem [intro!]: "~ (Var(v) <: t) ==> Idem([(v,t)])"
+by (simp add: vars_iff_occseq Idem_iff srange_iff empty_iff_all_not)
+
+lemma Unifier_Idem_subst: 
+  "[| Idem(r); Unifier s (t<|r) (u<|r) |]  
+   ==> Unifier (r <> s) (t <| r) (u <| r)"
+by (simp add: Idem_def Unifier_def comp_subst_subst)
+
+lemma Idem_comp:
+     "[| Idem(r);  Unifier s (t <| r) (u <| r);  
+         !!q. Unifier q (t <| r) (u <| r) ==> s <> q =$= q  
+      |] ==> Idem(r <> s)"
+apply (frule Unifier_Idem_subst, blast) 
+apply (force simp add: Idem_def subst_eq_iff)
+done
+
+
 end