[ 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).
+interpretation "natural plus" 'plus x y = (plus x y).
theorem plus_n_O: \forall n:nat. n = n+O.
intros.elim n.