intros n; elim n.
intros p q Hle; inversion Hle.
clear n; intros n.
intros Hrec p q Hle; case (le_gt_dec (S p) (S q)).
simpl in |- *.
intros Hle'; rewrite (le_minus_O p q).
CaseEq (q - p).
intros Heq_minus; exists p.
simpl in |- *; split; auto with arith.
rewrite <- plus_n_O.
apply le_antisym; auto with arith.
apply minus_O_le.
auto.
intros q' Heq_minus; elim (Hrec p q').
intros d; simpl in |- *; case (Qpositive_i (Qpositive_c (S p) (S q') n));
repeat rewrite <- (mult_comm (S d)); intros p'' q'' (Heq1, Heq2).
exists d; split.
exact Heq1.
rewrite (le_plus_minus (S p) (S q)).
simpl in |- *.
rewrite Heq_minus; rewrite Heq2.
simpl in |- *.
replace (S (p + q'' * S d)) with (S p + q'' * S d).
rewrite Heq1.
simpl in |- *.
ring.
simpl in |- *; auto.
auto with arith.
apply le_S_n.
rewrite plus_n_Sm.
apply le_trans with (S p + S q).
apply plus_le_compat_l.
apply le_n_S.
rewrite <- Heq_minus; apply minus_le.
exact Hle.
auto with arith.
intros Hgt; simpl in |- *; CaseEq (p - q).
intros H; elim (gt_not_le _ _ Hgt).
apply le_n_S.
apply minus_O_le.
exact H.
intros p'.
intros Heq_minus; simpl in |- *; elim (Hrec p' q).
intros d; case (Qpositive_i (Qpositive_c (S p') (S q) n)).
simpl in |- *; intros p'' q'' (Heq1, Heq2).
exists d; split; auto.
rewrite (le_plus_minus (S q) (S p)); simpl in |- *.
rewrite Heq_minus.
replace (S (q + S p')) with (S q + S p').
rewrite Heq2; rewrite Heq1; ring.
simpl in |- *; auto.
auto with arith.
rewrite <- Heq_minus.
replace (p - q) with (S p - S q).
rewrite <- (plus_comm (S q)).
rewrite <- (le_plus_minus (S q) (S p)).
apply le_trans with (S p + q).
auto with arith.
apply le_S_n; rewrite plus_n_Sm.
exact Hle.
auto with arith.
auto.
Qed.

Theorem construct_correct2' :
forall n p q : nat,
1 <= p ->
1 <= q ->
p + q <= n ->
exists d : nat,
p = fst (Qpositive_i (Qpositive_c p q n)) * S d /\
q = snd (Qpositive_i (Qpositive_c p q n)) * S d.