X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fground_2%2Flib%2Farith.ma;h=e3ec5c5040847cd64f141efd9aede61dcee4f658;hb=1083ac3b1acac5f1ac1fa40a9a417dd9d268dced;hp=dde95e8a7267d844ab844a0861e9ce1a044b480f;hpb=ff612dc35167ec0c145864c9aa8ae5e1ebe20a48;p=helm.git

diff --git a/matita/matita/contribs/lambdadelta/ground_2/lib/arith.ma b/matita/matita/contribs/lambdadelta/ground_2/lib/arith.ma
index dde95e8a7..e3ec5c504 100644
--- a/matita/matita/contribs/lambdadelta/ground_2/lib/arith.ma
+++ b/matita/matita/contribs/lambdadelta/ground_2/lib/arith.ma
@@ -57,6 +57,13 @@ lemma plus_SO: ∀n. n + 1 = ↑n.
 lemma minus_plus_m_m_commutative: ∀n,m:nat. n = m + n - m.
 // qed-.
 
+lemma plus_n_2: ∀n. n + 2 = n + 1 + 1.
+// qed.
+
+lemma arith_l: ∀x. 1 = 1-x+(x-(x-1)).
+* // #x >minus_S_S >minus_S_S <minus_O_n <minus_n_O //
+qed.
+
 (* Note: uses minus_minus_comm, minus_plus_m_m, commutative_plus, plus_minus *)
 lemma plus_minus_minus_be: ∀x,y,z. y ≤ z → z ≤ x → (x - z) + (z - y) = x - y.
 #x #z #y #Hzy #Hyx >plus_minus // >commutative_plus >plus_minus //
@@ -69,9 +76,6 @@ qed-.
 fact plus_minus_minus_be_aux: ∀i,x,y,z. y ≤ z → z ≤ x → i = z - y → x - z + i = x - y.
 /2 width=1 by plus_minus_minus_be/ qed-.
 
-lemma plus_n_2: ∀n. n + 2 = n + 1 + 1.
-// qed.
-
 lemma le_plus_minus: ∀m,n,p. p ≤ n → m + n - p = m + (n - p).
 /2 by plus_minus/ qed-.
 
@@ -143,6 +147,9 @@ fact le_repl_sn_trans_aux: ∀x,y,z:nat. x ≤ z → y = x → y ≤ z.
 lemma monotonic_le_minus_l2: ∀x1,x2,y,z. x1 ≤ x2 → x1 - y - z ≤ x2 - y - z.
 /3 width=1 by monotonic_le_minus_l/ qed.
 
+lemma minus_le_trans_sn: ∀x1,x2. x1 ≤ x2 → ∀x. x1-x ≤ x2.
+/2 width=3 by transitive_le/ qed.
+
 (* Note: this might interfere with nat.ma *)
 lemma monotonic_lt_pred: ∀m,n. m < n → 0 < m → pred m < pred n.
 #m #n #Hmn #Hm whd >(S_pred … Hm)