X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=helm%2Fsoftware%2Fmatita%2Flibrary%2Fnat%2Fplus.ma;h=e8b5f6d29e258cee77866c26a470f6cc4119bef5;hb=10f29fdd78ee089a9a94446207b543d33d6c851c;hp=d595dad19113cb6626ec4e58cc1e8a2d389be2b1;hpb=55b82bd235d82ff7f0a40d980effe1efde1f5073;p=helm.git

diff --git a/helm/software/matita/library/nat/plus.ma b/helm/software/matita/library/nat/plus.ma
index d595dad19..e8b5f6d29 100644
--- a/helm/software/matita/library/nat/plus.ma
+++ b/helm/software/matita/library/nat/plus.ma
@@ -36,6 +36,11 @@ simplify.reflexivity.
 simplify.apply eq_f.assumption.
 qed.
 
+theorem plus_n_SO : \forall n:nat. S n = n+(S O).
+intro.rewrite > plus_n_O.
+apply plus_n_Sm.
+qed.
+
 theorem sym_plus: \forall n,m:nat. n+m = m+n.
 intros.elim n.
 simplify.apply plus_n_O.