Consider the following premises. s_1 <-> t. ~s_4. s_4 or ~s_1. Can we infer t from them? If possible, name the inference rules being used at each step.
 From s_4 or ~s_1 we can infer s_1 -> s_4 via rewriting. From s_1 -> s_4, ~s_4 we can infer ~s_1 via modus tollens. Finally, from s_1 <-> t, ~s_1 we can infer ~t via biconditional elimination, which contradicts t. Therefore, the answer is no.