intros p q p' q' n n' H H0 H1.
elim (construct_correct2 _ _ _ H).
intros d (Heq1, Heq2).
elim (construct_correct2 _ _ _ H0).
intros d' (Heq3, Heq4).
elim (interp_non_zero (Qpositive_c (S p) (S q) (S n))).
intros p0 Hex1; elim Hex1; intros q0 Heq5; clear Hex1.
elim (interp_non_zero (Qpositive_c (S p') (S q') (S n'))).
intros p'0 Hex1; elim Hex1; intros q'0 Heq6; clear Hex1.
elim (interp_reduced_fraction (Qpositive_c (S p) (S q) (S n))); intros a Hex1;
elim Hex1; intros b; clear Hex1.
rewrite Heq6 in Heq4; rewrite Heq6 in Heq3; rewrite Heq5 in Heq2;
rewrite Heq5 in Heq1; rewrite Heq5; unfold fst, snd in |- *;
intros Heq7.
generalize H1; rewrite Heq1; rewrite Heq2; rewrite Heq3; rewrite Heq4;
unfold fst, snd in |- *; clear H1; intros H1.
unfold fst, snd in Heq1, Heq2, Heq3, Heq4.
cut (S p0 * S q'0 = S p'0 * S q0).
intros Heq8.
cut (S p'0 = Z.abs_nat (a * S p'0 + b * S q'0) * S p0).
intros Heq9.
cut (S q'0 = Z.abs_nat (a * S p'0 + b * S q'0) * S q0).
intros Heq10.
cut (exists d'' : nat, Z.abs_nat (a * S p'0 + b * S q'0) = S d'').
intros Hex; elim Hex; intros d'' Heq11; rewrite Heq11 in Heq9;
rewrite Heq11 in Heq10.
replace (S p0 * S d) with (S (d + p0 * S d)).
replace (S q0 * S d) with (S (d + q0 * S d)).
rewrite
(construct_correct3 n n (d + p0 * S d) (d + q0 * S d) (S p0) (S q0) d)
.
replace (S p'0 * S d') with (S (d' + p'0 * S d')).
replace (S q'0 * S d') with (S (d' + q'0 * S d')).
symmetry  in |- *.
apply construct_correct3 with (d := d' + d'' * S d').
replace (S (d' + p'0 * S d')) with (S p'0 * S d').
rewrite Heq9; ring.
auto.
replace (S (d' + q'0 * S d')) with (S q'0 * S d').
rewrite Heq10; ring.
auto.
replace (S (d' + q'0 * S d')) with (S q'0 * S d').
replace (S (d' + p'0 * S d')) with (S p'0 * S d').
rewrite <- Heq3; rewrite <- Heq4.
exact H0.
auto.
auto.
apply le_trans with (S p + S q).
rewrite Heq1; rewrite Heq2.
rewrite <- mult_plus_distr_r.
rewrite mult_comm; simpl in |- *; auto with arith.
assumption.
auto.
auto.
rewrite (mult_comm (S d)); auto.
rewrite (mult_comm (S d)); auto.
replace (S (d + q0 * S d)) with (S q0 * S d).
replace (S (d + p0 * S d)) with (S p0 * S d).
rewrite <- Heq1; rewrite <- Heq2.
exact H.
auto.
auto.
apply le_trans with (S p + S q).
rewrite Heq1; rewrite Heq2.
rewrite <- mult_plus_distr_r.
rewrite mult_comm; simpl in |- *; auto with arith.
assumption.
auto.
auto.
CaseEq (Z.abs_nat (a * S p'0 + b * S q'0)).
intros Dummy; rewrite Dummy in Heq10; simpl in Heq10; discriminate Heq10.
intros d'' Heq; exists d''; auto.
rewrite <- (absolu_inj_nat (S q0)).
pattern (S q'0) at 1 in |- *; rewrite <- (absolu_inj_nat (S q'0)).
rewrite <- absolu_mult.
apply f_equal with (f := Z.abs_nat).
pattern (Z_of_nat (S q'0)) at 1 in |- *; rewrite <- Zmult_1_r.
rewrite <- Heq7.
replace (S q'0 * (a * S p0 + b * S q0))%Z with
(S p0 * S q'0 * a + S q'0 * (b * S q0))%Z.
rewrite <- (Znat.inj_mult (S p0)).
rewrite Heq8.
rewrite Znat.inj_mult; ring.
ring.
rewrite <- (absolu_inj_nat (S p0)).
pattern (S p'0) at 1 in |- *; rewrite <- absolu_inj_nat.
rewrite <- absolu_mult.
apply f_equal with (f := Z.abs_nat).
pattern (Z_of_nat (S p'0)) at 1 in |- *; rewrite <- Zmult_1_r.
rewrite <- Heq7.
replace (S p'0 * (a * S p0 + b * S q0))%Z with
(S p'0 * S q0 * b + S p'0 * (a * S p0))%Z.
rewrite <- (Znat.inj_mult (S p'0)).
rewrite <- Heq8.
rewrite Znat.inj_mult; ring.
ring.
apply mult_reg_l with (d' + d * S d').
replace (S (d' + d * S d')) with (S d * S d').
transitivity (S p0 * S d * (S q'0 * S d')).
ring.
rewrite H1.
ring.
auto.
Qed.

Theorem construct_correct4' :
forall p q p' q' n n' : nat,
1 <= p ->
1 <= q ->
1 <= p' ->
1 <= q' ->
p + q <= n ->
p' + q' <= n' -> p * q' = p' * q -> Qpositive_c p q n = Qpositive_c p' q' n'.