progress.

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

diff --git a/helm/software/matita/library/nat/binomial.ma b/helm/software/matita/library/nat/binomial.ma
index 9505761488e3dd9568d51036ff877471c21215de..1a341032032b95c317863801601446727cbd983a 100644 (file)
--- a/helm/software/matita/library/nat/binomial.ma
+++ b/helm/software/matita/library/nat/binomial.ma
@@ -141,6 +141,28 @@ rewrite > (lt_to_lt_to_eq_div_div_times_times ? ? (S k)) in ⊢ (? ? ? (? % ?))
  apply lt_times;apply lt_O_fact]
 qed.
 
+theorem lt_O_bc: \forall n,m. m \le n \to O < bc n m.
+intro.elim n
+  [apply (le_n_O_elim ? H).
+   simplify.apply le_n
+  |elim (le_to_or_lt_eq ? ? H1)
+    [generalize in match H2.cases m;intro
+      [rewrite > bc_n_O.apply le_n
+      |rewrite > bc1
+        [apply (trans_le ? (bc n1 n2))
+          [apply H.apply le_S_S_to_le.apply lt_to_le.assumption
+          |apply le_plus_n_r
+          ]
+        |apply le_S_S_to_le.assumption
+        ]
+      ]
+    |rewrite > H2.
+     rewrite > bc_n_n.
+     apply le_n
+    ]
+  ]
+qed.
+
 theorem exp_plus_sigma_p:\forall a,b,n.
 exp (a+b) n = sigma_p (S n) (\lambda k.true) 
   (\lambda k.(bc n k)*(exp a (n-k))*(exp b k)).