intros a p q; case p; simpl in |- *; auto.
intros H'.
change
(minuspf (pO A n) (pX a q) =
pX (multTerm (A:=A) multA (n:=n) (invTerm (A:=A) invA (n:=n) (T1 A1 n)) a)
(minuspf (pO A n) q)) in |- *.
rewrite (minuspf_pOmults_eq (pX a q)); simpl in |- *; auto.
rewrite (minuspf_pOmults_eq q); simpl in |- *; auto.
intros a0 l H'.
change
(minuspf (pX a0 l) (pX a q) =
pX (invTerm (A:=A) invA (n:=n) a) (minuspf (pX a0 l) q))
in |- *.
rewrite <- (minuspf_inv2_eq a0 a l q); auto.
apply (canonical_pX_order A A0 eqA) with (l := l); auto.
Qed.
Hint Resolve inv_prop.

Theorem invTerm_T1_multTerm_T1 :
eqTerm (A:=A) eqA (n:=n)
(multTerm (A:=A) multA (n:=n) (invTerm (A:=A) invA (n:=n) (T1 A1 n))
(invTerm (A:=A) invA (n:=n) (T1 A1 n))) (T1 A1 n).