Consider the following premises. ~r_6. p_14 <-> t. p_14 -> r_6. u <-> t. Can we infer u from them?
 From p_14 <-> t we can infer t -> p_14. From t -> p_14, p_14 -> r_6 we can infer t -> r_6. From t -> r_6, ~r_6 we can infer ~t. Finally, from u <-> t, ~t we can infer ~u, which contradicts u. Therefore, the answer is no.