unfold included in |- *.
simpl in |- *.
intros G A H H' x H'0; try assumption.
elim H'0; intros x0; clear H'0.
generalize x; clear x.
elim x0.
intros c; try assumption.
elim c.
simpl in |- *.
intros y subtype_prf x H'0; elim H'0; intros H'1 H'2; try exact H'2;
clear H'0.
apply in_part_comp_l with y; auto with algebra.
intros f H'0 f0 H'1 x H'2; elim H'2; intros H'3 H'4; try exact H'4; clear H'2.
simpl in H'4.
apply
in_part_comp_l
with
(sgroup_law G (FG_lift_fun (inj_part A) f) (FG_lift_fun (inj_part A) f0));
auto with algebra.
simpl in |- *.
intros x H'0; elim H'0; intros H'1 H'2; try exact H'2; clear H'0.
apply in_part_comp_l with (monoid_unit G); auto with algebra.
intros f H'0 x H'1; try assumption.
elim H'1; intros H'2 H'3; simpl in H'3; clear H'1.
apply in_part_comp_l with (group_inverse G (FG_lift_fun (inj_part A) f));
auto with algebra.
Qed.

(* Specifications: *)
Lemma generated_group_prop_included :
forall (G : GROUP) (A : part_set G), included A (generated_group A).