Definition critical A B :=
[/\ A \char B,
Frattini A \subset 'Z(A),
[~: B, A] \subset 'Z(A)
& 'C_B(A) = 'Z(A)].
Definition special A := Frattini A = 'Z(A) /\  A^`(1) = 'Z(A).
Definition extraspecial A := special A /\ prime #|'Z(A)|.
Definition SCN B := [set A : {group gT} | A <| B & 'C_B(A) == A].
Definition SCN_at n B := [set A in SCN B | n <= 'r(A)].
End Defs.
Arguments charsimple {gT} A%g.
Arguments Frattini {gT} A%g.
Arguments Fitting {gT} A%g.
Arguments critical {gT} A%g B%g.
Arguments special {gT} A%g.
Arguments extraspecial {gT} A%g.
Arguments SCN {gT} B%g.
Arguments SCN_at {gT} n%N B%g.
Notation "''Phi' ( A )" := (Frattini A)
(at level 8, format "''Phi' ( A )") : group_scope.
Notation "''Phi' ( G )" := (Frattini_group G) : Group_scope.
Notation "''F' ( G )" := (Fitting G)
(at level 8, format "''F' ( G )") : group_scope.
Notation "''F' ( G )" := (Fitting_group G) : Group_scope.
Notation "''SCN' ( B )" := (SCN B)
(at level 8, format "''SCN' ( B )") : group_scope.
Notation "''SCN_' n ( B )" := (SCN_at n B)
(at level 8, n at level 2, format "''SCN_' n ( B )") : group_scope.
Section PMax.
Variables (gT : finGroupType) (p : nat) (P M : {group gT}).
Hypothesis pP : p.-group P.

Lemma p_index_maximal : M \subset P -> prime #|P : M| -> maximal M P.
End PMax.