Section Homg.
Implicit Types rT gT aT : finGroupType.
Definition homg rT aT (C : {set rT}) (D : {set aT}) :=
[exists (f : {ffun aT -> rT} | morphic D f), f @: D == C].

Lemma leq_homg rT aT (C : {set rT}) (G : {group aT}) :
homg C G -> #|C| <= #|G|.