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_6, if x_6 were a server, then x_6 is not sleeping. For all x_6, x_6 will sleep. There is at least one x_6 for which x_6 is a police officer. For all x_6, x_6 is a server or x_6 will play tennis.
For all x_6, x_6 is not a server can be inferred via the universal modus tollens rule. There is at least one x_6 for which x_6 is a police officer and x_6 will sleep can be inferred via the existential conjunction rule. There is at least one x_6 for which x_6 will sleep and x_6 is a police officer can be inferred via the existential conjunction rule.