Section ExtraspecialFormspace.
Variable G : {group gT}.
Hypotheses (pG : p.-group G) (esG : extraspecial G).
Let p_pr := extraspecial_prime pG esG.
Let oZ := card_center_extraspecial pG esG.
Let p_gt1 := prime_gt1 p_pr.
Let p_gt0 := prime_gt0 p_pr.
End ExtraspecialFormspace.

(* This is B & G, Theorem 4.15, as done in Aschbacher (23.8) *)
Lemma critical_extraspecial R S :
p.-group R -> S \subset R -> extraspecial S -> [~: S, R] \subset S^`(1) ->
S \* 'C_R(S) = R.