Section IsogAbelem.
Variables (aT rT : finGroupType) (G : {group aT}) (H : {group rT}).
Hypothesis isoGH : G \isog H.

Lemma p_rank_p'quotient G H :
(p : nat)^'.-group H -> G \subset 'N(H) -> 'r_p(G / H) = 'r_p(G).