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_7, x_7 is a taxi driver. For all x_7, if x_7 were a taxi driver, then x_7 is a server. For all x, if x were a server, then x is listening to a song.
For all x_7, x_7 is a server can be inferred via the universal modus ponens rule.