What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? ~r_4. r_1 -> r_4. ~R_21(f_2). forall x_21: R_21(x_21) or S_21(x_21).
~r_1. ~r_4 and ~R_21(f_2). ~R_21(f_2) and ~r_4.