intros a b H' H'0.
apply
(eqTerm_trans _ _ _ _ _ _ _ _ _ cs n)
with (y := plusTerm (A:=A) plusA (n:=n) a (invTerm (A:=A) invA (n:=n) b));
auto.
apply (eqTerm_sym _ _ _ _ _ _ _ _ _ cs n); auto.
apply zeroP_plusTermr with (1 := cs); auto.
apply (eqT_trans A n) with (y := b); auto.
apply zeroP_invTerm_zeroP with (1 := cs); auto.
Qed.
Hint Resolve minusTerm_zeroP minusTerm_zeroP_r.

Theorem minusP_pO_is_eqP :
forall p q r : list (Term A n),
minusP p q r -> eqP A eqA n r (pO A n) -> eqP A eqA n p q.