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 z_3, z_3 is a server. For all z_3, if z_3 listens to a song, then z_3 is writing a letter. There is at least one z_3 for which z_3 will listen to a song.
There is at least one z_3 for which z_3 will write a letter can be inferred via the existential modus ponens rule. There is at least one z_3 for which z_3 will listen to a song and z_3 is a server can be inferred via the existential conjunction rule. Some servers will listen to a song can be inferred via the existential conjunction rule.