Consider the following premises. s_4 <-> p. p or ~s_2. ~p_13. p_13 <-> s_4. Can we infer s_2 from them? If possible, name the inference rules being used at each step.
 From p_13 <-> s_4, ~p_13 we can infer ~s_4 via biconditional elimination. From s_4 <-> p, ~s_4 we can infer ~p via biconditional elimination. From p or ~s_2 we can infer s_2 -> p via rewriting. Finally, from s_2 -> p, ~p we can infer ~s_2 via modus tollens, which contradicts s_2. Therefore, the answer is no.