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_3, if y_3 plays tennis, then y_3 is a soldier. For all y_3, if y_3 were a soldier, then y_3 is playing tennis. For all x_8, x_8 is a soldier.
For all y_3, y_3 will play tennis if and only if y_3 is a soldier can be inferred via the universal biconditional introduction rule. For all y_3, y_3 is a soldier if and only if y_3 will play tennis can be inferred via the universal biconditional introduction rule.