Section Dihedral_extension.
Variable p : nat.
Hypotheses (p_gt1 : p > 1) (even_p : 2 %| p).
Local Notation ED := [set: gsort (Extremal.gtype q p q.-1)].
End Dihedral_extension.
End DihedralGroup.

Lemma involutions_gen_dihedral gT (x y : gT) :
let G := <<[set x; y]>> in
#[x] = 2 -> #[y] = 2 -> x != y -> G \isog 'D_#|G|.