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: For all x_4, x_4 will play squash if and only if x_4 will take a plane. For all x_4, if x_4 plays squash, then x_4 is not cooking. There is at least one x_4 for which x_4 will cook.
There is at least one x_4 for which x_4 will not play squash can be inferred via the existential modus tollens rule. For all x_4, if x_4 plays squash, then x_4 is taking a plane can be inferred via the universal biconditional elimination rule. For all x_4, if x_4 takes a plane, then x_4 is playing squash can be inferred via the universal biconditional elimination rule.