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: There is at least one x_9 for which x_9 is a server if and only if x_9 will listen to a song. For all x_9, if x_9 reads a book, then x_9 is a server. For all x_9, x_9 is an astronaut or x_9 will read a book. For all x_9, if x_9 were an astronaut, then x_9 is a server.
For all x_9, x_9 is a server can be inferred via the universal disjunction elimination rule. There is at least one x_9 for which if x_9 were a server, then x_9 is listening to a song can be inferred via the existential biconditional elimination rule. There is at least one x_9 for which if x_9 listens to a song, then x_9 is a server can be inferred via the existential biconditional elimination rule.