minus in nat.ma

[helm.git] / helm / software / matita / library / nat / compare.ma

diff --git a/helm/software/matita/library/nat/compare.ma b/helm/software/matita/library/nat/compare.ma
index 78dc50318197c3dbc449c50d3e757e868aec527d..4c44c74e0b61e8e84faea821e7b771b8dab56759 100644 (file)
--- a/helm/software/matita/library/nat/compare.ma
+++ b/helm/software/matita/library/nat/compare.ma
@@ -12,8 +12,6 @@
 (*                                                                        *)
 (**************************************************************************)
 
-set "baseuri" "cic:/matita/nat/compare".
-
 include "datatypes/bool.ma".
 include "datatypes/compare.ma".
 include "nat/orders.ma".
@@ -126,6 +124,23 @@ apply nat_elim2; intros; simplify
   ]
 qed.
 
+theorem leb_true_to_le:\forall n,m.
+leb n m = true \to (n \le m).
+intros 2.
+apply leb_elim
+  [intros.assumption
+  |intros.destruct H1.
+  ]
+qed.
+
+theorem leb_false_to_not_le:\forall n,m.
+leb n m = false \to \lnot (n \le m).
+intros 2.
+apply leb_elim
+  [intros.destruct H1
+  |intros.assumption
+  ]
+qed.
 (*
 theorem decidable_le: \forall n,m. n \leq m \lor n \nleq m. 
 intros.
@@ -302,3 +317,14 @@ apply ((H H3)).
 apply ((H1 H3)).
 apply ((H2 H3)).
 qed.
+
+inductive cmp_cases (n,m:nat) : CProp ≝
+  | cmp_le : n ≤ m → cmp_cases n m
+  | cmp_gt : m < n → cmp_cases n m.
+
+lemma cmp_nat: ∀n,m.cmp_cases n m.
+intros; generalize in match (nat_compare_to_Prop n m);
+cases (nat_compare n m); intros;
+[constructor 1;apply lt_to_le|constructor 1;rewrite > H|constructor 2]
+try assumption; apply le_n;
+qed.