Consider the following premises. For all x_11, x_11 is a carpenter if and only if x_11 is sad. For all x_11, if x_11 plays squash, then x_11 is a musician. For all x_11, x_11 is not a carpenter. For all x_11, if x_11 were a musician, then x_11 is sad. For all x_11, if x_11 were a taxi driver, then x_11 is playing squash. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_11 for which x_11 is a taxi driver.
 From the fact that for all x_11, x_11 is a carpenter if and only if x_11 is sad, and that for all x_11, x_11 is not a carpenter we can infer that for all x_11, x_11 is not sad via universal biconditional elimination. From the fact that for all x_11, if x_11 were a musician, then x_11 is sad, and that for all x_11, x_11 is not sad we can infer that for all x_11, x_11 is not a musician via universal modus tollens. From the fact that for all x_11, if x_11 plays squash, then x_11 is a musician, and that for all x_11, x_11 is not a musician we can infer that for all x_11, x_11 will not play squash via universal modus tollens. Finally, from the fact that for all x_11, if x_11 were a taxi driver, then x_11 is playing squash, and that for all x_11, x_11 will not play squash we can infer that for all x_11, x_11 is not a taxi driver via universal modus tollens, which contradicts that There is at least one x_11 for which x_11 is a taxi driver. Therefore, the answer is no.