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: Q_4(y) -> U(y). forall y: Q_4(y) -> U(y). exists y: U(y) -> Q_4(y).
exists y: U(y) <-> Q_4(y) can be inferred via the existential biconditional introduction rule. exists y: U(y) <-> Q_4(y) can be inferred via the existential biconditional introduction rule. exists y: Q_4(y) <-> U(y) can be inferred via the existential biconditional introduction rule. exists y: Q_4(y) <-> U(y) can be inferred via the existential biconditional introduction rule.