intros a b H'.
apply (eqT_trans A n) with (y := b); auto.
apply (eqT_trans A n) with (y := multTerm (A:=A) multA (n:=n) (T1 A1 n) b);
auto.
apply (T1_eqT A A1 eqA); auto.
Qed.

(* Specifications: *)
Lemma multTerm_invTerm_T1_eqT_comp :
forall a b : Term A n,
eqT a b ->
eqT a
(multTerm (A:=A) multA (n:=n) (invTerm (A:=A) invA (n:=n) (T1 A1 n)) b).