intros a b c; case a; case b; case c; simpl in |- *; auto.
intros a1 m1 a2 m2 a3 m3; split; auto.
apply
(eqA_trans _ _ _ _ _ _ _ _ _ cs) with (plusA (multA a1 a3) (multA a1 a2));
auto.
apply (eqA_trans _ _ _ _ _ _ _ _ _ cs) with (multA a1 (plusA a3 a2)); auto.
Qed.

Theorem multTerm_plusTerm_dist_r :
forall a b c : Term,
eqTerm (plusTerm (multTerm c a) (multTerm c b)) (multTerm c (plusTerm a b)).