intros a b; case a; case b; simpl in |- *; auto.
intuition.
apply (eqA_trans _ _ _ _ _ _ _ _ _ cs) with (y := A0); auto.
apply (eqA_sym _ _ _ _ _ _ _ _ _ cs); auto.
Qed.

Theorem zeroP_dec : forall x : Term, {zeroP x} + {~ zeroP x}.
intros x; case x; simpl in |- *.