propagating the arithmetics library, partial commit

[helm.git] / matita / matita / contribs / lambdadelta / ground / arith / pnat_plus.ma

diff --git a/matita/matita/contribs/lambdadelta/ground/arith/pnat_plus.ma b/matita/matita/contribs/lambdadelta/ground/arith/pnat_plus.ma
index 8fd6b5c47034a1cf6783ab55845b669dce8e9513..1ff7afbb4c1945ff56bfca1781eca4a586177ce4 100644 (file)
--- a/matita/matita/contribs/lambdadelta/ground/arith/pnat_plus.ma
+++ b/matita/matita/contribs/lambdadelta/ground/arith/pnat_plus.ma
@@ -49,3 +49,25 @@ lemma pplus_assoc: associative … pplus.
 #p #q #r elim r -r //
 #r #IH <pplus_succ_dx <pplus_succ_dx <IH -IH //
 qed.
+
+(* Basic inversions *********************************************************)
+
+lemma eq_inv_unit_pplus (p) (q): 𝟏 = p + q → ⊥.
+#p #q elim q -q
+[ <pplus_one_dx #H destruct
+| #q #_ <pplus_succ_dx #H destruct
+]
+qed-.
+
+lemma eq_inv_pplus_unit (p) (q):
+      p + q = 𝟏 → ⊥.
+/2 width=3 by eq_inv_unit_pplus/ qed-.
+
+lemma eq_inv_pplus_bi_dx (r) (p) (q): p + r = q + r → p = q.
+#r elim r -r /3 width=1 by eq_inv_psucc_bi/
+qed-.
+
+lemma eq_inv_pplus_bi_sn (r) (p) (q): r + p = r + q → p = q.
+#r #p #q <pplus_comm <pplus_comm in ⊢ (???%→?);
+/2 width=2 by eq_inv_pplus_bi_dx/
+qed-.