What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: q_4 or S(f). q_4 <-> P(f). forall y: S(y) -> P(y).
R_1(f) -> q_4 can be inferred via the rewriting rule. q_4 -> P(f) can be inferred via the biconditional elimination rule. P(f) -> q_4 can be inferred via the biconditional elimination rule.