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 sleeps, then x_9 is a server. For all x_9, x_9 is a server if and only if x_9 will sleep. For all x_9, if x_9 were a server, then x_9 is sleeping.
For all x_9, x_9 will sleep if and only if x_9 is a server can be inferred via the universal biconditional introduction rule. For all x_9, x_9 is a server if and only if x_9 will sleep can be inferred via the universal biconditional introduction rule. For all x_9, if x_9 were a server, then x_9 is sleeping can be inferred via the universal biconditional elimination rule. For all x_9, if x_9 sleeps, then x_9 is a server can be inferred via the universal biconditional elimination rule.