Consider the following premises. ~u_4. u_4 <-> w. t or w. ~t or w_1. Can we infer w_1 from them? If possible, name the inference rules being used at each step.
 From t or w, ~t or w_1 we can infer w or w_1 via resolution. From u_4 <-> w, ~u_4 we can infer ~w via biconditional elimination. Finally, from w or w_1, ~w we can infer w_1 via disjunctive syllogism. Therefore, the answer is yes.