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 z, z is a doctor if and only if z will play tennis. If Thomas were a janitor, then James is a doctor. James is not playing tennis.
For all z, if z were a doctor, then z is playing tennis can be inferred via the universal biconditional elimination rule. For all z, if z plays tennis, then z is a doctor can be inferred via the universal biconditional elimination rule.