generalized the theorem zless_zero_nat to zless_nat_eq_int_zless, and
reorganized

--- a/src/HOL/Integ/Int.ML	Wed Sep 08 15:40:39 1999 +0200
+++ b/src/HOL/Integ/Int.ML	Wed Sep 08 15:41:30 1999 +0200
@@ -230,6 +230,20 @@
 by Auto_tac; 
 qed "neg_nat"; 
 
+Goal "(m < nat z) = (int m < z)";
+by (case_tac "neg z" 1);
+by (etac (not_neg_nat RS subst) 2);
+by (auto_tac (claset(), simpset() addsimps [neg_nat])); 
+by (auto_tac (claset() addDs [order_less_trans], 
+	      simpset() addsimps [neg_eq_less_int0])); 
+qed "zless_nat_eq_int_zless";
+
+Goal "z <= int 0 ==> nat z = 0"; 
+by (auto_tac (claset(), 
+	      simpset() addsimps [order_le_less, neg_eq_less_int0, 
+				  zle_def, neg_nat])); 
+qed "nat_le_int0"; 
+
 (*An alternative condition is  int 0 <= w  *)
 Goal "int 0 < z ==> (nat w < nat z) = (w < z)";
 by (stac (zless_int RS sym) 1);
@@ -241,24 +255,12 @@
 by (blast_tac (claset() addIs [order_less_trans]) 1);
 val lemma = result();
 
-Goal "z <= int 0 ==> nat z = 0"; 
-by (auto_tac (claset(), 
-	      simpset() addsimps [order_le_less, neg_eq_less_int0, 
-				  zle_def, neg_nat])); 
-qed "nat_le_int0"; 
-
 Goal "(nat w < nat z) = (int 0 < z & w < z)";
 by (case_tac "int 0 < z" 1);
 by (auto_tac (claset(), 
 	      simpset() addsimps [lemma, nat_le_int0, linorder_not_less])); 
 qed "zless_nat_conj";
 
-Goal "(0 < nat z) = (int 0 < z)";
-by (stac (order_refl RS nat_le_int0 RS sym) 1);
-by (stac zless_nat_conj 1);
-by (Simp_tac 1);
-qed "zless_zero_nat";
-
 
 (* a case theorem distinguishing non-negative and negative int *)