Consider the following premises. ~u. p -> t. s_3 or p. u <-> s_3. Can we infer ~t from them? If possible, name the inference rules being used at each step.
 From u <-> s_3, ~u we can infer ~s_3 via biconditional elimination. From s_3 or p, ~s_3 we can infer p via disjunctive syllogism. Finally, from p -> t, p we can infer t via modus ponens, which contradicts ~t. Therefore, the answer is no.