Consider the following premises. r_2 -> s_4. s or r_2. s <-> s_4. forall y: U(y). Can we infer ~s_4 from them?
 From s <-> s_4 we can infer s -> s_4. From forall y: U(y) we can infer U(a_18). Finally, from s -> s_4, r_2 -> s_4, s or r_2 we can infer s_4, which contradicts ~s_4. Therefore, the answer is no.