proposition: Lemma card_ffun : #|fT| = #|rT| ^ #|aT|.
proof: Proof. by rewrite -card_ffun_on; apply/esym/eq_card=> f; apply/forallP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype tuple)