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_8, x_8 will take a plane. For all x_9, if x_9 were a server, then x_9 is taking a plane. For all x_9, if x_9 takes a plane, then x_9 is a server.
For all x_9, x_9 is a server if and only if x_9 will take a plane can be inferred via the universal biconditional introduction rule. For all x_9, x_9 will take a plane if and only if x_9 is a server can be inferred via the universal biconditional introduction rule.