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: forall y: P_4(y) -> S(y). forall y: S(y) -> P_4(y). exists y: P_4(y).
exists y: S(y) can be inferred via the existential modus ponens rule. forall y: P_4(y) <-> S(y) can be inferred via the universal biconditional introduction rule. forall y: S(y) <-> P_4(y) can be inferred via the universal biconditional introduction rule.