What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If it snows, then Barbara is a janitor. It is not snowing. If Barbara were a janitor, then it is snowing. For all y, y will write a letter if and only if y is a janitor.
Barbara is not a janitor. For all y, if y writes a letter, then y is a janitor. For all y, if y were a janitor, then y is writing a letter.