Consider the following premises. ~t. u_2 <-> t. u -> u_2. u or ~u_2. Can we infer u from them?
 From u_2 <-> t, ~t we can infer ~u_2. From u or ~u_2 we can infer u_2 -> u. From u -> u_2, u_2 -> u we can infer u <-> u_2. Finally, from u <-> u_2, ~u_2 we can infer ~u, which contradicts u. Therefore, the answer is no.