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: ~U(y). forall y: R_1(y) -> U(y). r_3 <-> R_1(a). forall y: U(y) -> R_1(y).
r_3 -> R_1(a) can be inferred via the biconditional elimination rule. R_1(a) -> r_3 can be inferred via the biconditional elimination rule. forall y: ~R_1(y) can be inferred via the universal modus tollens rule. forall y: R_1(y) <-> U(y) can be inferred via the universal biconditional introduction rule. forall y: U(y) <-> R_1(y) can be inferred via the universal biconditional introduction rule.