Consider the following premises. q -> w. w -> R_21(a_21). forall x_21: ~R_21(x_21). R_21(a_21) -> w. p -> q. Can we infer p from them? If possible, name the inference rules being used at each step.
 From forall x_21: ~R_21(x_21) we can infer ~R_21(a_21) via universal instantiation. From R_21(a_21) -> w, w -> R_21(a_21) we can infer R_21(a_21) <-> w via biconditional introduction. From R_21(a_21) <-> w, ~R_21(a_21) we can infer ~w via biconditional elimination. From q -> w, ~w we can infer ~q via modus tollens. Finally, from p -> q, ~q we can infer ~p via modus tollens, which contradicts p. Therefore, the answer is no.