What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all y, y is not a mechanic. For all y, y is a janitor if and only if y is a mechanic. For all y, y is a janitor or y is a sailor.
For all y, if y were a janitor, then y is a mechanic. For all y, if y were a mechanic, then y is a janitor. For all y, y is not a janitor.