X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=helm%2Fsoftware%2Fmatita%2Flibrary%2Fnat%2Fminus.ma;h=92324aae7610481c69fdc15a3fef5e5da8db0fb2;hb=5c10d402b5de7233bc83d7f685b274832e383212;hp=f1178107a28d4f742a14942642b7daf650e97009;hpb=a180bddcd4a8f35de3d7292162ba05d0077723aa;p=helm.git

diff --git a/helm/software/matita/library/nat/minus.ma b/helm/software/matita/library/nat/minus.ma
index f1178107a..92324aae7 100644
--- a/helm/software/matita/library/nat/minus.ma
+++ b/helm/software/matita/library/nat/minus.ma
@@ -13,8 +13,6 @@
 (**************************************************************************)
 
 
-set "baseuri" "cic:/matita/nat/minus".
-
 include "nat/le_arith.ma".
 include "nat/compare.ma".
 
@@ -26,8 +24,7 @@ let rec minus n m \def
 	[O \Rightarrow (S p)
         | (S q) \Rightarrow minus p q ]].
 
-(*CSC: the URI must disappear: there is a bug now *)
-interpretation "natural minus" 'minus x y = (cic:/matita/nat/minus/minus.con x y).
+interpretation "natural minus" 'minus x y = (minus x y).
 
 theorem minus_n_O: \forall n:nat.n=n-O.
 intros.elim n.simplify.reflexivity.
@@ -78,13 +75,12 @@ qed.
 
 theorem minus_plus_m_m: \forall n,m:nat.n = (n+m)-m.
 intros 2.
-generalize in match n.
-elim m.
+elim m in n ⊢ %.
 rewrite < minus_n_O.apply plus_n_O.
-elim n2.simplify.
+elim n1.simplify.
 apply minus_n_n.
 rewrite < plus_n_Sm.
-change with (S n3 = (S n3 + n1)-n1).
+change with (S n2 = (S n2 + n)-n).
 apply H.
 qed.
 
@@ -271,10 +267,16 @@ qed.
 lemma lt_to_lt_O_minus : \forall m,n.
   n < m \to O < m - n.
 intros.  
-unfold. apply le_plus_to_minus_r. unfold in H. rewrite > sym_plus. 
+unfold. apply le_plus_to_minus_r. unfold in H.
+cut ((S n ≤ m) = (1 + n ≤ m)) as applyS;
+  [ rewrite < applyS; assumption;
+  | demodulate; reflexivity. ]
+(*
+rewrite > sym_plus. 
 rewrite < plus_n_Sm. 
 rewrite < plus_n_O. 
 assumption.
+*)
 qed.  
 
 theorem lt_minus_to_plus: \forall n,m,p. (lt n (p-m)) \to (lt (n+m) p).
@@ -287,6 +289,56 @@ rewrite < plus_n_Sm.
 apply H.apply H1.
 qed.
 
+theorem lt_O_minus_to_lt: \forall a,b:nat.
+O \lt b-a \to a \lt b.
+intros.
+rewrite > (plus_n_O a).
+rewrite > (sym_plus a O).
+apply (lt_minus_to_plus O  a b).
+assumption.
+qed.
+
+theorem lt_minus_to_lt_plus:
+\forall n,m,p. n - m < p \to n < m + p.
+intros 2.
+apply (nat_elim2 ? ? ? ? n m)
+  [simplify.intros.autobatch.
+  |intros 2.rewrite < minus_n_O.
+   intro.assumption
+  |intros.
+   simplify.
+   cut (n1 < m1+p)
+    [autobatch
+    |apply H.
+     apply H1
+    ]
+  ]
+qed.
+
+theorem lt_plus_to_lt_minus:
+\forall n,m,p. m \le n \to n < m + p \to n - m < p.
+intros 2.
+apply (nat_elim2 ? ? ? ? n m)
+  [simplify.intros 3.
+   apply (le_n_O_elim ? H).
+   simplify.intros.assumption
+  |simplify.intros.assumption.
+  |intros.
+   simplify.
+   apply H
+    [apply le_S_S_to_le.assumption
+    |apply le_S_S_to_le.apply H2
+    ]
+  ]
+qed. 
+
+theorem minus_m_minus_mn: \forall n,m. n\le m \to n=m-(m-n).
+intros.
+apply sym_eq.
+apply plus_to_minus.
+autobatch.
+qed.
+
 theorem distributive_times_minus: distributive nat times minus.
 unfold distributive.
 intros.
@@ -311,10 +363,13 @@ theorem distr_times_minus: \forall n,m,p:nat. n*(m-p) = n*m-n*p
 theorem eq_minus_plus_plus_minus: \forall n,m,p:nat. p \le m \to (n+m)-p = n+(m-p).
 intros.
 apply plus_to_minus.
+lapply (plus_minus_m_m ?? H); demodulate. reflexivity.
+(*
 rewrite > sym_plus in \vdash (? ? ? %).
 rewrite > assoc_plus.
 rewrite < plus_minus_m_m.
 reflexivity.assumption.
+*)
 qed.
 
 theorem eq_minus_minus_minus_plus: \forall n,m,p:nat. (n-m)-p = n-(m+p).