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 z_3 for which z_3 is a server if and only if z_3 will cook. For all z_3, if z_3 were a server, then z_3 is cooking. For all z_3, if z_3 cooks, then z_3 is a server.
For all z_3, z_3 is a server if and only if z_3 will cook can be inferred via the universal biconditional introduction rule. For all z_3, z_3 will cook if and only if z_3 is a server can be inferred via the universal biconditional introduction rule. There is at least one z_3 for which if z_3 were a server, then z_3 is cooking can be inferred via the existential biconditional elimination rule. There is at least one z_3 for which if z_3 cooks, then z_3 is a server can be inferred via the existential biconditional elimination rule.