intros l1 l2 l3 H'; elim H'; auto.
intros a1 a2 l4 l5 l6 H'0 H'1 H'2 H'3 H'4.
apply order_minusP with (l1 := l4) (l2 := pX a2 l5); auto.
apply canonical_cons; auto.
apply canonical_nzeroP with (ltM := ltM) (p := l4); auto.
apply H'2; auto.
apply canonical_imp_canonical with (a := a1); auto.
intros a1 a2 l4 l5 l6 H'0 H'1 H'2 H'3 H'4 H'5.
apply H'1; auto.
apply canonical_imp_canonical with (a := a1); auto.
apply canonical_imp_canonical with (a := a2); auto.
intros a1 a2 l4 l5 l6 H'0 H'1 H'2 H'3 H'4 H'5.
apply order_minusP with (l1 := l4) (l2 := l5); auto.
apply canonical_pX_eqT with (a := a1); auto.
apply (eqT_sym A n); apply minusTerm_eqT; auto.
apply canonical_pX_eqT with (a := a2); auto.
apply (eqT_trans A n) with (y := a1); apply (eqT_sym A n); auto.
apply minusTerm_eqT; auto.
apply H'1.
apply canonical_imp_canonical with (a := a1); auto.
apply canonical_imp_canonical with (a := a2); auto.
intros a1 a2 l4 l5 l6 H'0 H'1 H'2 H'3 H'4.
apply order_minusP with (l1 := pX a1 l4) (l2 := l5); auto.
apply canonical_pX_eqT with (a := a2); auto.
apply canonical_cons; auto.
apply canonical_nzeroP with (ltM := ltM) (p := l5); auto.
apply nZero_invTerm_nZero with (1 := cs); auto.
apply canonical_nzeroP with (ltM := ltM) (p := l5); auto.
apply canonical_pX_eqT with (a := a2); auto.
apply nZero_invTerm_nZero with (1 := cs); auto.
apply canonical_nzeroP with (ltM := ltM) (p := l5); auto.
apply H'2; auto.
apply canonical_imp_canonical with (a := a2); auto.
Qed.

Theorem canonical_minuspf :
forall l1 l2 : list (Term A n),
canonical A0 eqA ltM l1 ->
canonical A0 eqA ltM l2 -> canonical A0 eqA ltM (minuspf l1 l2).