proposition: Lemma Ngcd_nz1 a b: natp a -> natp b-> (a <> \0c \/ b <> \0c) -> Ngcd a b <> \0c.
proof: Proof. by move => az bz h gnz; move: (Ngcd_nz az bz gnz) => [a0 b0]; case: h. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)