[ O \Rightarrow m
| (S p) \Rightarrow S (plus p m) ].
+(*CSC: the URI must disappear: there is a bug now *)
interpretation "natural plus" 'plus x y = (cic:/matita/nat/plus/plus.con x y).
-alias symbol "plus" (instance 0) = "natural plus".
theorem plus_n_O: \forall n:nat. n = n+O.
intros.elim n.