intros b H' H'0;
apply (eqA_trans _ _ _ _ _ _ _ _ _ cs) with (y := plusA A0 (invA A0));
auto.
apply (eqA_trans _ _ _ _ _ _ _ _ _ cs) with (y := invA A0); auto.
apply (eqA_trans _ _ _ _ _ _ _ _ _ cs) with (y := plusA (invA A0) A0); auto.
apply (eqA_sym _ _ _ _ _ _ _ _ _ cs); auto.
Qed.

Theorem invTerm_invol : forall a : Term, eqTerm a (invTerm (invTerm a)).
intros a; case a; simpl in |- *; auto.