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