Section InjmAbelem.
Variables (aT rT : finGroupType) (D G : {group aT}) (f : {morphism D >-> rT}).
Hypotheses (injf : 'injm f) (sGD : G \subset D).
Let defG : invm injf @* (f @* G) = G := morphim_invm injf sGD.

Lemma exponent_injm : exponent (f @* G) = exponent G.