intros p.
rewrite <- (minusP_pO_refl_eq p (minuspf p (pO A n))); auto.
Qed.

Theorem Opm_ind :
forall (P : list (Term A n) -> list (Term A n) -> Prop)
(p q : list (Term A n)),
(forall p : list (Term A n), P (pO A n) p) ->
(forall p : list (Term A n), P p (pO A n)) ->
(forall (a b : Term A n) (p q : list (Term A n)),
P (pX a p) q -> ltT ltM a b -> P (pX a p) (pX b q)) ->
(forall (a b : Term A n) (p q : list (Term A n)),
P p (pX b q) -> ltT ltM b a -> P (pX a p) (pX b q)) ->
(forall (a b : Term A n) (p q : list (Term A n)),
P p q -> eqT a b -> P (pX a p) (pX b q)) ->
forall p q : list (Term A n), P p q.