Consider the following premises. t -> ~q_12. w <-> r_2. ~r_2. q_12. Can we infer w from them? If possible, name the inference rules being used at each step.
 From t -> ~q_12, q_12 we can infer ~t via modus tollens. Finally, from w <-> r_2, ~r_2 we can infer ~w via biconditional elimination, which contradicts w. Therefore, the answer is no.