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_9, if x_9 were a cashier, then x_9 is running. For all x_9, x_9 is a cashier or x_9 is happy. For all x_9, x_9 will go running if and only if x_9 is happy. For all x_9, if x_9 goes running, then x_9 is a cashier.
For all x_9, x_9 is a cashier if and only if x_9 will go running can be inferred via the universal biconditional introduction rule. For all x_9, x_9 will go running if and only if x_9 is a cashier can be inferred via the universal biconditional introduction rule. For all x_9, if x_9 goes running, then x_9 is happy can be inferred via the universal biconditional elimination rule. For all x_9, if x_9 were happy, then x_9 is running can be inferred via the universal biconditional elimination rule.