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 politician if and only if x_9 is a taxi driver. For all x_9, if x_9 plays tennis, then x_9 is a server. For all x_9, x_9 is not a politician. For all x_9, if x_9 were a server, then x_9 is a taxi driver.
For all x_9, if x_9 plays tennis, then x_9 is a taxi driver can be inferred via the universal transitivity rule. There is at least one x_9 for which if x_9 were a politician, then x_9 is a taxi driver can be inferred via the existential biconditional elimination rule. There is at least one x_9 for which if x_9 were a taxi driver, then x_9 is a politician can be inferred via the existential biconditional elimination rule. There is at least one x_9 for which x_9 is not a taxi driver can be inferred via the existential biconditional elimination rule.