Section ExtremalClass.
Variables (gT : finGroupType) (G : {group gT}).
Inductive extremal_group_type :=
ModularGroup | Dihedral | SemiDihedral | Quaternion | NotExtremal.
Definition index_extremal_group_type c :=
match c with
| ModularGroup => 0
| Dihedral => 1
| SemiDihedral => 2
| Quaternion => 3
| NotExtremal => 4
end%N.
Definition enum_extremal_groups :=
[:: ModularGroup; Dihedral; SemiDihedral; Quaternion].
End ExtremalClass.

(* This is Aschbacher (23.9) *)
Theorem symplectic_type_group_structure gT p (G : {group gT}) :
p.-group G -> (forall X : {group gT}, X \char G -> abelian X -> cyclic X) ->
exists2 E : {group gT}, E :=: 1 \/ extraspecial E
& exists R : {group gT},
[/\ cyclic R \/ [/\ p = 2, extremal2 R & #|R| >= 16],
E \* R = G
& E :&: R = 'Z(E)].