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 nurse if and only if x_9 is a taxi driver. For all x_9, x_9 is a nurse or x_9 is not a taxi driver.
For all x_9, if x_9 were a taxi driver, then x_9 is a nurse can be inferred via the universal rewriting rule. There is at least one x_9 for which if x_9 were a nurse, 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 nurse can be inferred via the existential biconditional elimination rule.