Consider the following premises. p_11 <-> p. p_11 <-> R_7(a_7). ~p. forall x_7: R_7(x_7) <-> S_7(x_7). Can we infer S_7(a_7) from them? If possible, name the inference rules being used at each step.
 From p_11 <-> p, ~p we can infer ~p_11 via biconditional elimination. From forall x_7: R_7(x_7) <-> S_7(x_7) we can infer R_7(a_7) <-> S_7(a_7) via universal instantiation. From p_11 <-> R_7(a_7), ~p_11 we can infer ~R_7(a_7) via biconditional elimination. Finally, from R_7(a_7) <-> S_7(a_7), ~R_7(a_7) we can infer ~S_7(a_7) via biconditional elimination, which contradicts S_7(a_7). Therefore, the answer is no.