intros P H' H'0 H'1 H'2 H'3 H'4 H'5 p; elim p; auto.
intros a l H'6 q; elim q; auto.
intros a0 l0 H'7;
(case (ltT_dec A n ltM ltM_dec a a0);
[ intros temp; case temp; clear temp | idtac ];
intros test); change (P (pX a l) (pX a0 l0)) in |- *;
auto.
Qed.

(* Specifications: *)
Theorem minuspf_eq_inv1 :
forall (a : Term A n) (p q : list (Term A n)),
canonical A0 eqA ltM (pX a p) ->
canonical A0 eqA ltM (pX a q) ->
eqP A eqA n (pX a (minuspf p q)) (minuspf (pX a p) q).