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, x_9 is a cashier. For all x_9, x_9 is a poet or x_9 will drink water. For all x_9, if x_9 were a poet, then x_9 is not a cashier. For all x_9, x_9 is happy.
For all x_9, x_9 is not a poet can be inferred via the universal modus tollens rule. For all x_9, x_9 is a cashier and x_9 is happy can be inferred via the universal conjunction rule. For all x_9, x_9 is happy and x_9 is a cashier can be inferred via the universal conjunction rule.