X-Git-Url: http://matita.cs.unibo.it/gitweb/?p=helm.git;a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fground%2Farith%2Fnat_plus.ma;h=2f0f4b658a7251e0f5b69ea023505dfdbb647b6e;hp=40beec972819238df4a5bdd75ed92e403d48d436;hb=dbc57c92512c04b3fd88f8289bb8dbe99b2f90e0;hpb=baa54e5db0fb93c4242dd1b67a5018ca63206cf6

diff --git a/matita/matita/contribs/lambdadelta/ground/arith/nat_plus.ma b/matita/matita/contribs/lambdadelta/ground/arith/nat_plus.ma
index 40beec972..2f0f4b658 100644
--- a/matita/matita/contribs/lambdadelta/ground/arith/nat_plus.ma
+++ b/matita/matita/contribs/lambdadelta/ground/arith/nat_plus.ma
@@ -80,7 +80,7 @@ lemma nplus_one_sn (n): ↑n = 𝟏 + n.
 #n <nplus_comm // qed.
 
 lemma nplus_succ_shift (m) (n): ↑m + n = m + ↑n.
-// qed-.
+// qed.
 
 (*** assoc_plus1 *)
 lemma nplus_plus_comm_12 (o) (m) (n): m + n + o = n + (m + o).
@@ -89,11 +89,11 @@ lemma nplus_plus_comm_12 (o) (m) (n): m + n + o = n + (m + o).
 (*** plus_plus_comm_23 *)
 lemma nplus_plus_comm_23 (o) (m) (n): o + m + n = o + n + m.
 #o #m #n >nplus_assoc >nplus_assoc <nplus_comm in ⊢ (??(??%)?); //
-qed-.
+qed.
 
 (* Basic inversions *********************************************************)
 
-(*** plus_inv_O3 zero_eq_plus *) 
+(*** zero_eq_plus *)
 lemma eq_inv_zero_nplus (m) (n): 𝟎 = m + n → ∧∧ 𝟎 = m & 𝟎 = n.
 #m #n @(nat_ind_succ … n) -n
 [ /2 width=1 by conj/
@@ -102,6 +102,11 @@ lemma eq_inv_zero_nplus (m) (n): 𝟎 = m + n → ∧∧ 𝟎 = m & 𝟎 = n.
 ]
 qed-.
 
+(*** plus_inv_O3 *)
+lemma eq_inv_nplus_zero (m) (n):
+      m + n = 𝟎 → ∧∧ 𝟎 = m & 𝟎 = n.
+/2 width=1 by eq_inv_zero_nplus/ qed-.
+
 (*** injective_plus_l *)
 lemma eq_inv_nplus_bi_dx (o) (m) (n): m + o = n + o → m = n.
 #o @(nat_ind_succ … o) -o /3 width=1 by eq_inv_nsucc_bi/