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, if y_1 plays tennis, then y_1 is a cashier. For all x_13, x_13 will work if and only if x_13 will play tennis. For all x_13, if x_13 sleeps, then x_13 is playing tennis. For all x_13, x_13 will sleep or x_13 will work.
For all x_13, if x_13 works, then x_13 is playing tennis can be inferred via the universal biconditional elimination rule. For all x_13, if x_13 plays tennis, then x_13 is working can be inferred via the universal biconditional elimination rule.