Open Scope Z_scope.
intros.
pols.
auto.
Qed.
intros.
pols.
auto.
Qed.
intros.
pols.
auto with zarith.
Qed.
intros.
pols.
auto.
Qed.

Theorem pols_test5:
forall x y z, x + y * (y + z) = 2 * z ->  2 * x + y * (y + z) = (x + z) + z.