Section char.
Variables (n : nat) (gT rT : finGroupType) (D G : {group gT}).
Fact abelian_type_subproof G :
{H : {group gT} & abelian G -> {x | #[x] = exponent G & <[x]> \x H = G}}.
Fixpoint abelian_type_rec n G :=
if n is n'.+1 then if abelian G && (G :!=: 1) then
exponent G :: abelian_type_rec n' (tag (abelian_type_subproof G))
else [::] else [::].
Definition abelian_type (A : {set gT}) := abelian_type_rec #|A| <<A>>.
Definition homocyclic A := abelian A && constant (abelian_type A).

Lemma max_card_abelian G :
abelian G -> #|G| <= exponent G ^ 'r(G) ?= iff homocyclic G.