intros Q p q H'; elim H'; auto.
intros a b nZb p0 q0 r H'0 H'1 H'2 H'3.
apply
eqp_imp_canonical
with
(1 := cs)
(p := spminusf A A0 A1 eqA invA minusA multA divA eqA_dec n ltM ltM_dec a
b nZb p0 q0); auto.
apply canonical_spminusf with (1 := cs); auto.
apply canonical_imp_canonical with (a := a); auto.
apply canonical_imp_canonical with (a := b); auto.
apply inPolySet_imp_canonical with (L := Q); auto.
intros a b p0 q0 H'0 H'1 H'2 H'3.
apply eqp_imp_canonical with (1 := cs) (p := pX a q0); auto.
cut (canonical A0 eqA ltM p0);
[ intros C1 | apply canonical_imp_canonical with (a := a) ];
auto.
apply ltP_pX_canonical; auto.
apply canonical_nzeroP with (ltM := ltM) (p := p0); auto.
apply ltP_trans with (y := p0); auto.
apply ltP_reduce with (Q := Q); auto.
apply (canonical_pX_ltP A A0 eqA); auto.
Qed.

Theorem reduce_eqp_com :
forall (Q : list (poly A0 eqA ltM)) (p q r s : list (Term A n)),
reduce Q p q ->
canonical A0 eqA ltM p -> eqP A eqA n p r -> eqP A eqA n q s -> reduce Q r s.