Section MorphAbelem.
Variables (aT rT : finGroupType) (D : {group aT}) (f : {morphism D >-> rT}).
Implicit Types (G H E : {group aT}) (A B : {set aT}).

Lemma morphim_pnElem p n G E :
E \in 'E_p^n(G) -> {m | m <= n & (f @* E)%G \in 'E_p^m(f @* G)}.