intros a b c; case a; case b; case c; simpl in |- *; auto.
intuition.
apply (eqA_sym _ _ _ _ _ _ _ _ _ cs).
apply plusA_assoc with (1 := cs).
Qed.

Theorem eqTerm_plusTerm_comp :
forall a b c d : Term,
eqT a c ->
eqT b d -> eqTerm a b -> eqTerm c d -> eqTerm (plusTerm a c) (plusTerm b d).