src/ZF/perm.thy
 changeset 0 a5a9c433f639 child 124 858ab9a9b047
```--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/ZF/perm.thy	Thu Sep 16 12:20:38 1993 +0200
@@ -0,0 +1,36 @@
+(*  Title: 	ZF/perm
+    ID:         \$Id\$
+    Author: 	Lawrence C Paulson, Cambridge University Computer Laboratory
+    Copyright   1991  University of Cambridge
+
+The theory underlying permutation groups
+  -- Composition of relations, the identity relation
+  -- Injections, surjections, bijections
+  -- Lemmas for the Schroeder-Bernstein Theorem
+*)
+
+Perm = ZF +
+consts
+    O    	::      "[i,i]=>i"      (infixr 60)
+    id  	::      "i=>i"
+    inj,surj,bij::      "[i,i]=>i"
+
+rules
+
+    (*composition of relations and functions; NOT Suppes's relative product*)
+    comp_def	"r O s == {xz : domain(s)*range(r) . \
+\                  		EX x y z. xz=<x,z> & <x,y>:s & <y,z>:r}"
+
+    (*the identity function for A*)
+    id_def	"id(A) == (lam x:A. x)"
+
+    (*one-to-one functions from A to B*)
+    inj_def      "inj(A,B) == { f: A->B. ALL w:A. ALL x:A. f`w=f`x --> w=x}"
+
+    (*onto functions from A to B*)
+    surj_def	"surj(A,B) == { f: A->B . ALL y:B. EX x:A. f`x=y}"
+
+    (*one-to-one and onto functions*)
+    bij_def	"bij(A,B) == inj(A,B) Int surj(A,B)"
+
+end```