intros p q r H'; generalize r; elim H'; clear r H'.
intros r H' H'0 H'1; rewrite <- pO_pluspf_inv1; auto.
intros ma mb p0 q0 H' H'0 H'1 r H'2 H'3 H'4.
cut (canonical A0 eqA ltM p0);
[ intros C0 | apply canonical_imp_canonical with (a := ma) ];
auto.
cut (canonical A0 eqA ltM q0);
[ intros C1 | apply canonical_imp_canonical with (a := mb) ];
auto.
cut (~ zeroP (A:=A) A0 eqA (n:=n) ma);
[ intros nZ0 | apply (canonical_nzeroP _ A0 eqA n ltM) with (p := p0) ];
auto.
cut (~ zeroP (A:=A) A0 eqA (n:=n) mb);
[ intros nZ1 | apply (canonical_nzeroP _ A0 eqA n ltM) with (p := q0) ];
auto.
generalize H'4; elim r; clear H'4 r.
intros H'4; rewrite <- pO_pluspf_inv2; rewrite <- pO_pluspf_inv2; auto.
intros a l H'4 H'5.
cut (canonical A0 eqA ltM l);
[ intros C2 | apply canonical_imp_canonical with (a := a) ];
auto.
cut (~ zeroP (A:=A) A0 eqA (n:=n) a);
[ intros nZ2 | apply (canonical_nzeroP _ A0 eqA n ltM) with (p := l) ];
auto.
change
(eqP A eqA n (pluspf (pX ma p0) (pX a l)) (pluspf (pX mb q0) (pX a l)))
in |- *.
case (ltT_dec A n ltM ltM_dec ma a); [ intros H0; case H0; clear H0 | idtac ];
intros H0.
cut (ltT ltM mb a); [ intros Or0 | idtac ].
rewrite <- (pluspf_inv2_eq ma a p0 l); auto.
rewrite <- (pluspf_inv2_eq mb a q0 l); auto.
apply eqT_compat_ltTl with (b := ma); auto.
apply (eqTerm_imp_eqT A eqA n); auto.
cut (ltT ltM a mb); [ intros Or0 | idtac ]; auto.
rewrite <- (pluspf_inv1_eq ma a p0 l); auto.
rewrite <- (pluspf_inv1_eq mb a q0 l); auto.
apply eqT_compat_ltTr with (b := ma); auto.
apply (eqTerm_imp_eqT A eqA n); auto.
cut
(eqTerm eqA (plusTerm (A:=A) plusA (n:=n) ma a)
(plusTerm (A:=A) plusA (n:=n) mb a)); [ intros eqTerm0 | idtac ];
auto.
case (zeroP_dec A A0 eqA eqA_dec n (plusTerm (A:=A) plusA (n:=n) ma a));
intros Z0.
rewrite <- (pluspf_inv3a_eq ma a p0 l); auto.
rewrite <- (pluspf_inv3a_eq mb a q0 l); auto.
apply (eqT_trans A n) with (y := ma); auto.
apply (eqTerm_imp_eqT A eqA n); auto.
apply (eqTerm_sym _ _ _ _ _ _ _ _ _ cs n); auto.
apply
zeroP_comp_eqTerm with (1 := cs) (a := plusTerm (A:=A) plusA (n:=n) ma a);
auto.
rewrite <- (pluspf_inv3b_eq ma a p0 l); auto.
rewrite <- (pluspf_inv3b_eq mb a q0 l); auto.
apply (eqT_trans A n) with (y := ma); auto.
apply (eqTerm_imp_eqT A eqA n); auto.
apply (eqTerm_sym _ _ _ _ _ _ _ _ _ cs n); auto.
red in |- *; intros H'6; apply Z0.
apply
zeroP_comp_eqTerm with (1 := cs) (a := plusTerm (A:=A) plusA (n:=n) mb a);
auto.
apply plusTerm_comp_l with (1 := cs); auto.
change (eqT mb a) in |- *.
apply (eqT_trans A n) with (y := ma); auto.
apply (eqTerm_imp_eqT A eqA n); auto.
apply (eqTerm_sym _ _ _ _ _ _ _ _ _ cs n); auto.
apply (eqTerm_sym _ _ _ _ _ _ _ _ _ cs n); auto.
apply plusTerm_comp_l with (1 := cs); auto.
change (eqT mb a) in |- *.
apply (eqT_trans A n) with (y := ma); auto.
apply (eqTerm_imp_eqT A eqA n); auto.
apply (eqTerm_sym _ _ _ _ _ _ _ _ _ cs n); auto.
Qed.

Theorem eqp_pluspf_com_r :
forall p q r,
eqP A eqA n p q ->
canonical A0 eqA ltM p ->
canonical A0 eqA ltM q ->
canonical A0 eqA ltM r -> eqP A eqA n (pluspf r p) (pluspf r q).