Section fparts2_def.
Variable E : Setoid.
Definition disjoint (A B : part_set E) := Equal (inter A B) (empty E).
unfold disjoint in |- *.
intros A A' B B' H' H'0 H'1; try assumption.
apply Trans with (inter A B).
auto with *.
auto with *.
Qed.
intros A; case A; intros a pa; simpl in |- *.
unfold eq_part, empty in |- *; simpl in |- *.
intuition.
intros.
elim (H x); auto with *.
Qed.
unfold included, disjoint in |- *.
intros A B C H' H'0; try assumption.
apply not_in_empty.
unfold not in |- *; intros.
cut (in_part x (inter B C)).
generalize (empty_not_in (A:=inter B C) H'0).
unfold not in |- *; intros.
apply H0 with (x := x).
auto with *.
auto with *.
apply in_part_inter.
apply H'.
apply in_part_inter_l with C.
auto with *.
apply in_part_inter_r with A.
auto with *.
Qed.
intros A x; red in |- *.
unfold add_part in |- *.
auto with *.
Qed.
Hint Resolve included_add_part: algebra.
unfold not in |- *; intros.
cut (in_part x A \/ in_part x B).
intros H'; try assumption.
intuition.
auto with *.
Qed.
Hint Resolve union_not_in: algebra.
unfold disjoint in |- *.
unfold not in |- *; intros.
cut (in_part x (empty E)).
auto with *.
apply in_part_comp_r with (inter A B).
auto with *.
auto with *.
Qed.

Lemma cardinal_union_disjoint :
forall (a b : nat) (A B : part_set E),
cardinal A a -> cardinal B b -> disjoint A B -> cardinal (union A B) (a + b).