Consider the following premises. For all x_9, x_9 will play tennis or x_9 is not a taxi driver. There is at least one x_9 for which x_9 will work if and only if x_9 will play tennis. Can we infer the following from them? If we can, name the inference rule being used: For all x_9, the fact that x_9 were a taxi driver does not imply that x_9 is working.
 From the fact that there is at least one x_9 for which x_9 will work if and only if x_9 will play tennis we can infer that there is at least one x_9 for which if x_9 plays tennis, then x_9 is working via existential biconditional elimination. Finally, from the fact that for all x_9, x_9 will play tennis or x_9 is not a taxi driver we can infer that for all x_9, if x_9 were a taxi driver, then x_9 is playing tennis via universal rewriting, which contradicts that For all x_9, the fact that x_9 were a taxi driver does not imply that x_9 is working. Therefore, the answer is no.