End CardMorphism.

(* Specifications: *)
Lemma card_homg (aT rT : finGroupType) (G : {group aT}) (R : {group rT}) :
G \homg R -> #|G| %| #|R|.
Lemma card_cosetpre : #|coset H @*^-1 L| = (#|H| * #|L|)%N.