Consider the following premises. ~R_21(a_21). forall x_21: R_21(x_21) <-> S_21(x_21). s <-> p_13. p_13 <-> S_21(a_21). Can we infer ~s or q from them? If possible, name the inference rules being used at each step.
 From forall x_21: R_21(x_21) <-> S_21(x_21) we can infer R_21(a_21) <-> S_21(a_21) via universal instantiation. From R_21(a_21) <-> S_21(a_21), ~R_21(a_21) we can infer ~S_21(a_21) via biconditional elimination. From p_13 <-> S_21(a_21), ~S_21(a_21) we can infer ~p_13 via biconditional elimination. From s <-> p_13, ~p_13 we can infer ~s via biconditional elimination. Finally, from ~s we can infer ~s or q via addition. Therefore, the answer is yes.