we started the theory of delifting substitution ...

[helm.git] / matita / matita / lib / arithmetics / nat.ma

diff --git a/matita/matita/lib/arithmetics/nat.ma b/matita/matita/lib/arithmetics/nat.ma
index b937c077f12ad01a563bb984ba957a5c0ad5d868..edb99b8c0c9dac85517e253e9282d7f34597bd89 100644 (file)
--- a/matita/matita/lib/arithmetics/nat.ma
+++ b/matita/matita/lib/arithmetics/nat.ma
@@ -135,9 +135,6 @@ theorem injective_plus_r: ∀n:nat.injective nat nat (λm.n+m).
 theorem injective_plus_l: ∀n:nat.injective nat nat (λm.m+n). 
 /2/ qed.
 
-theorem not_eq_S: ∀n,m:nat. n ≠ m → S n ≠ S m.
-/2/ qed.
-
 theorem times_Sn_m: ∀n,m:nat. m+n*m = S n*m.
 // qed.
 
@@ -192,6 +189,9 @@ lemma plus_plus_comm_23: ∀x,y,z. x + y + z = x + z + y.
 
 (* Negated equalities *******************************************************)
 
+theorem not_eq_S: ∀n,m:nat. n ≠ m → S n ≠ S m.
+/2/ qed.
+
 theorem not_eq_O_S : ∀n:nat. 0 ≠ S n.
 #n @nmk #eqOS (change with (not_zero O)) >eqOS // qed.
 
@@ -242,7 +242,7 @@ theorem monotonic_le_plus_l:
 theorem le_plus: ∀n1,n2,m1,m2:nat. n1 ≤ n2  → m1 ≤ m2 
 → n1 + m1 ≤ n2 + m2.
 #n1 #n2 #m1 #m2 #len #lem @(transitive_le ? (n1+m2))
-/2/ qed-.
+/2/ qed.
 
 theorem le_plus_n :∀n,m:nat. m ≤ n + m.
 /2/ qed. 
@@ -299,6 +299,12 @@ theorem le_plus_to_minus_r: ∀a,b,c. a + b ≤ c → a ≤ c -b.
 #a #b #c #H @(le_plus_to_le_r … b) /2/
 qed.
 
+lemma lt_to_le: ∀x,y. x < y → x ≤ y.
+/2 width=2/ qed.
+
+lemma inv_eq_minus_O: ∀x,y. x - y = 0 → x ≤ y.
+// qed-.
+
 (* lt *)
 
 theorem transitive_lt: transitive nat lt.
@@ -402,14 +408,14 @@ theorem not_le_to_lt: ∀n,m. n ≰ m → m < n.
 @nat_elim2 #n
  [#abs @False_ind /2/
  |/2/
- |#m #Hind #HnotleSS @le_S_S /3/
+ |#m #Hind #HnotleSS @le_S_S @Hind /2/ 
  ]
 qed.
 
 (* not lt, le *)
 
 theorem not_lt_to_le: ∀n,m:nat. n ≮ m → m ≤ n.
-/4/ qed.
+#n #m #H @le_S_S_to_le @not_le_to_lt /2/ qed.
 
 theorem le_to_not_lt: ∀n,m:nat. n ≤ m → m ≮ n.
 #n #m #H @lt_to_not_le /2/ (* /3/ *) qed.
@@ -441,20 +447,24 @@ theorem increasing_to_le2: ∀f:nat → nat. increasing f →
 qed.
 
 lemma le_inv_plus_l: ∀x,y,z. x + y ≤ z → x ≤ z - y ∧ y ≤ z.
-/3 width=2/ qed-.
+/3/ qed-.
 
 lemma lt_inv_plus_l: ∀x,y,z. x + y < z → x < z ∧ y < z - x.
-/3 width=2/ qed-.
+/3/ qed-.
 
 lemma lt_or_ge: ∀m,n. m < n ∨ n ≤ m.
-#m #n elim (decidable_lt m n) /2 width=1/ /3 width=1/
+#m #n elim (decidable_lt m n) /2/ /3/
+qed-.
+
+lemma le_or_ge: ∀m,n. m ≤ n ∨ n ≤ m.
+#m #n elim (decidable_le m n) /2/ /4/
 qed-.
 
 (* More general conclusion **************************************************)
 
 theorem nat_ind_plus: ∀R:predicate nat.
                       R 0 → (∀n. R n → R (n + 1)) → ∀n. R n.
-/3 width=1 by nat_ind/ qed-.
+/3 by nat_ind/ qed-.
 
 theorem lt_O_n_elim: ∀n:nat. 0 < n → 
   ∀P:nat → Prop.(∀m:nat.P (S m)) → P n.
@@ -492,7 +502,7 @@ theorem le_n_O_to_eq : ∀n:nat. n ≤ 0 → 0=n.
 #n (cases n) // #a  #abs @False_ind /2/ qed.
 
 theorem le_to_le_to_eq: ∀n,m. n ≤ m → m ≤ n → n = m.
-@nat_elim2 /4/
+@nat_elim2 /4 by le_n_O_to_eq, monotonic_pred, eq_f, sym_eq/
 qed. 
 
 theorem increasing_to_injective: ∀f:nat → nat.
@@ -591,14 +601,19 @@ theorem increasing_to_le: ∀f:nat → nat.
 @(ex_intro ?? (S a)) /2/
 qed.
 
+(* thus is le_plus
 lemma le_plus_compatible: ∀x1,x2,y1,y2. x1 ≤ y1 → x2 ≤ y2 → x1 + x2 ≤ y1 + y2.
-/3 by le_minus_to_plus, monotonic_le_plus_r, transitive_le/ qed.
+#x1 #y1 #x2 #y2 #H1 #H2 /2/ @le_plus // /2/ /3 by le_minus_to_plus, monotonic_le_plus_r, transitive_le/ qed.
+*)
+
+lemma minus_le: ∀x,y. x - y ≤ x.
+/2 width=1/ qed.
 
 (* lt *)
 
 theorem not_eq_to_le_to_lt: ∀n,m. n≠m → n≤m → n<m.
 #n #m #Hneq #Hle cases (le_to_or_lt_eq ?? Hle) //
-#Heq /3/ qed-.
+#Heq @not_le_to_lt /2/ qed-.
 
 theorem lt_times_n_to_lt_l: 
 ∀n,p,q:nat. p*n < q*n → p < q.
@@ -630,6 +645,14 @@ theorem monotonic_lt_minus_l: ∀p,q,n. n ≤ q → q < p → q - n < p - n.
 @lt_plus_to_minus_r <plus_minus_m_m //
 qed.
 
+(* More compound conclusion *************************************************)
+
+lemma discr_minus_x_xy: ∀x,y. x = x - y → x = 0 ∨ y = 0.
+* /2 width=1/ #x * /2 width=1/ #y normalize #H 
+lapply (minus_le x y) <H -H #H
+elim (not_le_Sn_n x) #H0 elim (H0 ?) //
+qed-.
+
 (* Still more equalities ****************************************************)
 
 theorem eq_minus_O: ∀n,m:nat.
@@ -640,7 +663,7 @@ qed.
 theorem distributive_times_minus: distributive ? times minus.
 #a #b #c
 (cases (decidable_lt b c)) #Hbc
- [> eq_minus_O /2/ >eq_minus_O // 
+ [> eq_minus_O [2:/2/] >eq_minus_O // 
   @monotonic_le_times_r /2/
  |@sym_eq (applyS plus_to_minus) <distributive_times_plus 
   @eq_f (applyS plus_minus_m_m) /2/
@@ -673,6 +696,9 @@ qed.
 lemma minus_minus_m_m: ∀m,n. n ≤ m → m - (m - n) = n.
 /2 width=1/ qed.
 
+lemma minus_plus_plus_l: ∀x,y,h. (x + h) - (y + h) = x - y.
+// qed.
+
 (* Stilll more atomic conclusion ********************************************)
 
 (* le *)