intros A B0 B x H' H'0 H'1; try assumption.
apply in_eq_part.
intros x0 H'2; try assumption.
elim (classic (Equal x0 x)).
intros H'3; try assumption.
apply in_part_trans_eq with x; auto with *.
intros H'3; try assumption.
unfold add_part in |- *.
apply in_part_union_or.
left.
apply in_diff.
apply add_part_in_el_diff with x; auto with *.
apply in_part_comp_r with A; auto with *.
apply diff_in_l with B; auto with *.
apply diff_in_r with A; auto with *.
intros x0 H'2; try assumption.
apply in_diff.
apply in_part_comp_r with (add_part B0 x); auto with *.
elim (classic (Equal x0 x)).
intros H'3; try assumption.
apply in_part_trans_eq with x; auto with *.
intros H'3; try assumption.
unfold add_part in |- *.
apply in_part_union_or.
left.
unfold add_part in H'2.
elim (in_part_union H'2).
intros H'4; try assumption.
apply diff_in_l with B; auto with *.
intros H'4; try assumption.
absurd (in_part x0 (single x)); auto with *.
elim (classic (Equal x0 x)).
intros H'3; try assumption.
unfold not in |- *; intros.
unfold not in H'1.
apply H'1.
apply in_part_trans_eq with x0; auto with *.
intros H'3; try assumption.
apply diff_in_r with B0; auto with *.
apply add_part_in_el_diff with x; auto with *.
Qed.
Hint Resolve diff_add_part_not_in: algebra.

Lemma inter_add_part_not_in :
forall (A B0 B : part_set E) (x : E),
~ in_part x B0 ->
Equal A (add_part B0 x) -> ~ in_part x B -> Equal (inter B0 B) (inter A B).