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