Consider the following premises. s -> w_1. ~t_2. u <-> w_1. w_1 -> s. u -> t_2. Can we infer s from them?
 From w_1 -> s, s -> w_1 we can infer w_1 <-> s. From u -> t_2, ~t_2 we can infer ~u. From u <-> w_1, ~u we can infer ~w_1. Finally, from w_1 <-> s, ~w_1 we can infer ~s, which contradicts s. Therefore, the answer is no.