intros a p; elim p; auto.
intros q H' H'0; rewrite minuspf_pOmults_eq.
rewrite minuspf_pOmults_eq; simpl in |- *.
apply eqpP1; auto.
change
(eqTerm (A:=A) eqA (n:=n) (invTerm (A:=A) invA (n:=n) a)
(multTerm (A:=A) multA (n:=n) (invTerm (A:=A) invA (n:=n) (T1 A1 n)) a))
in |- *.
apply
(eqTerm_trans _ _ _ _ _ _ _ _ _ cs n)
with
(y := invTerm (A:=A) invA (n:=n)
(multTerm (A:=A) multA (n:=n) (T1 A1 n) a));
auto.
apply (eqTerm_sym _ _ _ _ _ _ _ _ _ cs n); auto.
intros a0 l H' q H'0 H'1.
change
(eqP A eqA n (pX (invTerm (A:=A) invA (n:=n) a) (minuspf (pX a0 l) q))
(minuspf (pX a0 l) (pX a q))) in |- *.
rewrite <- (minuspf_inv2_eq a0 a l q); auto.
apply (canonical_pX_order A A0 eqA) with (l := l); auto.
Qed.
Definition inv : list (Term A n) -> Term A n -> Term A n.
intros p; case p.
intros a;
exact
(multTerm (A:=A) multA (n:=n) (invTerm (A:=A) invA (n:=n) (T1 A1 n)) a).
intros a1 p1 a; exact (invTerm (A:=A) invA (n:=n) a).
Defined.

Theorem inv_prop :
forall (a : Term A n) (p q : list (Term A n)),
canonical A0 eqA ltM (pX a p) ->
minuspf p (pX a q) = pX (inv p a) (minuspf p q).