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 y_1, y_1 will not play tennis. There is at least one y_1 for which if y_1 plays tennis, then y_1 is a doctor. For all y_1, y_1 will play tennis if and only if y_1 is a doctor.
For all y_1, if y_1 plays tennis, then y_1 is a doctor can be inferred via the universal biconditional elimination rule. For all y_1, if y_1 were a doctor, then y_1 is playing tennis can be inferred via the universal biconditional elimination rule. For all y_1, y_1 is not a doctor can be inferred via the universal biconditional elimination rule.