Consider the following premises. For all x_4, x_4 is bored if and only if x_4 is a taxi driver. For all x_4, x_4 is a taxi driver. Can we infer the following from them? If we can, name the inference rule being used: For all x_4, x_4 is bored.
 From the fact that for all x_4, x_4 is bored if and only if x_4 is a taxi driver we can infer that for all x_4, if x_4 were a taxi driver, then x_4 is bored via universal biconditional elimination. Finally, from the fact that for all x_4, if x_4 were a taxi driver, then x_4 is bored, and that for all x_4, x_4 is a taxi driver we can infer that for all x_4, x_4 is bored via universal modus ponens. Therefore, the answer is yes.