proposition: Lemma Sphi_countable x y: countable_ordinal x -> countable_ordinal y -> countable_ordinal (Sphi x y).
proof: Proof. move => /aleph_oneP xa /aleph_oneP ya; apply/aleph_oneP. by apply:Sphi_bounded => //; apply: CIS_omega. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)