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: There is at least one y for which y will not take a plane. For all y, if y plays squash, then y is taking a plane. For all y, y will take a plane or y will not play squash. For all y, if y takes a plane, then y is playing squash.
There is at least one y for which y will not play squash can be inferred via the existential modus tollens rule. For all y, if y plays squash, then y is taking a plane can be inferred via the universal rewriting rule. For all y, y will play squash if and only if y will take a plane can be inferred via the universal biconditional introduction rule. For all y, y will take a plane if and only if y will play squash can be inferred via the universal biconditional introduction rule.