Consider the following premises. exists x_15: Q_15(x_15). forall x_15: U(x_15) <-> Q_15(x_15). forall x_15: S_3(x_15). Can we infer exists x_15: U(x_15) from them?
 From forall x_15: U(x_15) <-> Q_15(x_15) we can infer forall x_15: Q_15(x_15) -> U(x_15). Finally, from forall x_15: Q_15(x_15) -> U(x_15), exists x_15: Q_15(x_15) we can infer exists x_15: U(x_15). Therefore, the answer is yes.