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: For all y_1, if y_1 were a sailor, then y_1 is a janitor. For all y_1, y_1 is a janitor. For all y_1, if y_1 were a janitor, then y_1 is a sailor.
For all y_1, y_1 is a sailor can be inferred via the universal modus ponens rule. For all y_1, y_1 is a sailor if and only if y_1 is a janitor can be inferred via the universal biconditional introduction rule. For all y_1, y_1 is a janitor if and only if y_1 is a sailor can be inferred via the universal biconditional introduction rule.