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