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_9, x_9 is fast if and only if x_9 is a taxi driver. For all x_9, if x_9 were fast, then x_9 is a taxi driver. For all x_9, x_9 is a taxi driver.
For all x_9, if x_9 were fast, then x_9 is a taxi driver can be inferred via the universal biconditional elimination rule. For all x_9, if x_9 were a taxi driver, then x_9 is fast can be inferred via the universal biconditional elimination rule.