What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Joseph is not playing squash. For all y, if y takes a plane, then y is playing squash. If Joseph doesn't take a plane, then Elisabeth is a carpenter. For all y, if y plays squash, then y is taking a plane.
For all y, y will take a plane if and only if y will play squash. For all y, y will play squash if and only if y will take a plane.