diff -r 20b708827030 -r 5dfdc1464966 src/ZF/AC/first.ML
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/ZF/AC/first.ML	Thu May 18 11:51:23 1995 +0200
@@ -0,0 +1,41 @@
+(*  Title: 	ZF/AC/first.ML
+    ID:         $Id$
+    Author: 	Krzysztof Gr`abczewski
+
+Lemmas involving the first element of a well ordered set
+*)
+
+open first;
+
+goalw thy [first_def] "!!b. first(b,B,r) ==> b:B";
+by (fast_tac AC_cs 1);
+val first_is_elem = result();
+
+goalw thy [well_ord_def, wf_on_def, wf_def, exists_first_def, first_def]
+	"!!r. well_ord(A,r) ==> ALL B. (B<=A & B~=0) --> exists_first(B,r)";
+by (resolve_tac [allI] 1);
+by (resolve_tac [impI] 1);
+by (REPEAT (eresolve_tac [conjE,allE,disjE] 1));
+by (contr_tac 1);
+by (eresolve_tac [bexE] 1);
+by (resolve_tac [bexI] 1 THEN (atac 2));
+by (rewrite_goals_tac [tot_ord_def, linear_def]);
+by (fast_tac ZF_cs 1);
+val well_ord_imp_ex_first = result();
+
+goalw thy [well_ord_def, wf_on_def, wf_def, 	first_def] 
+	"!!r. [| well_ord(A,r); B<=A; B~=0 |] ==> (EX! b. first(b,B,r))";
+by (REPEAT (eresolve_tac [conjE,allE,disjE] 1));
+by (contr_tac 1);
+by (eresolve_tac [bexE] 1);
+by (res_inst_tac [("a","x")] ex1I 1);
+by (fast_tac ZF_cs 2);
+by (rewrite_goals_tac [tot_ord_def, linear_def]);
+by (fast_tac ZF_cs 1);
+val well_ord_imp_ex1_first = result();
+
+goal thy "!!r. [| well_ord(A,r); B<=A; B~=0 |] ==> (THE b. first(b,B,r)) : B";
+by (dresolve_tac [well_ord_imp_ex1_first] 1 THEN REPEAT (atac 1));
+by (resolve_tac [first_is_elem] 1);
+by (eresolve_tac [theI] 1);
+val the_first_in = result();