Consider the following premises. q_4 or r_3. r_3 -> p_3. p_3 <-> q_4. Can we infer p_3 from them? If possible, name the inference rules being used at each step.
 From p_3 <-> q_4 we can infer q_4 -> p_3 via biconditional elimination. Finally, from q_4 -> p_3, r_3 -> p_3, q_4 or r_3 we can infer p_3 via disjunction elimination. Therefore, the answer is yes.