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_6, if x_6 plays squash, then x_6 is not a doctor. For all x_6, x_6 will play squash if and only if x_6 will go running. For all x_6, x_6 is a doctor.
For all x_6, x_6 will not play squash can be inferred via the universal modus tollens rule. For all x_6, if x_6 plays squash, then x_6 is running can be inferred via the universal biconditional elimination rule. For all x_6, if x_6 goes running, then x_6 is playing squash can be inferred via the universal biconditional elimination rule.