intros A B H'; try assumption.
unfold included in |- *.
intros x H'0; try assumption.
elim H'0.
intros x0 H'1; try assumption.
apply in_image with (x := x0); auto with algebra.
red in H'.
elim H'1.
auto with algebra.
elim H'1; auto with algebra.
Qed.
Hint Resolve image_included: algebra.

Lemma image_comp :
forall A B : part_set E, Equal A B -> Equal (image A) (image B).