(* This program is free software; you can redistribute it and/or      *)
(* modify it under the terms of the GNU Lesser General Public License *)
(* as published by the Free Software Foundation; either version 2.1   *)
(* of the License, or (at your option) any later version.             *)
(*                                                                    *)
(* This program is distributed in the hope that it will be useful,    *)
(* but WITHOUT ANY WARRANTY; without even the implied warranty of     *)
(* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the      *)
(* GNU General Public License for more details.                       *)
(*                                                                    *)
(* You should have received a copy of the GNU Lesser General Public   *)
(* License along with this program; if not, write to the Free         *)
(* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA *)
(* 02110-1301 USA                                                     *)
Require Export Qpositive.
Definition Qpositive_plus (w w' : Qpositive) : Qpositive :=
let (p, q) := Qpositive_i w in
let (p', q') := Qpositive_i w' in
Qpositive_c (p * q' + p' * q) (q * q') (p * q' + p' * q + q * q').
intros w; elim (interp_non_zero w); intros p Hex; elim Hex; intros q Heq.
unfold Qpositive_plus in |- *.
replace (Qpositive_i One) with (1, 1).
rewrite Heq.
rewrite mult_1_r; rewrite mult_1_l.
rewrite (plus_comm (S q)).
replace (S p + S q + S q) with (S (p + S q + S q)).
rewrite (Qpositive_c_unfold1 p q).
rewrite (construct_correct w); auto with *.
auto.
auto.
auto.
Qed.
intros w w'; elim (interp_non_zero w); intros p Hex; elim Hex; intros q Heq;
clear Hex.
elim (interp_non_zero w'); intros p' Hex; elim Hex; intros q' Heq'; clear Hex.
unfold Qpositive_plus in |- *.
rewrite Heq; rewrite Heq'.
repeat rewrite (mult_comm (S q')).
repeat rewrite (mult_comm (S p')).
repeat rewrite (plus_comm (S p * S q')).
auto.
Qed.

Theorem Qpositive_plus_assoc :
forall w w' w'' : Qpositive,
Qpositive_plus (Qpositive_plus w w') w'' =
Qpositive_plus w (Qpositive_plus w' w'').