Consider the following premises. For all x_6, x_6 will listen to a song or x_6 is not an office clerk. For all x_6, x_6 will not listen to a song. There is at least one x_6 for which x_6 is happy if and only if x_6 is an office clerk. Can we infer the following from them? There is at least one x_6 for which x_6 is not happy.
 From the fact that for all x_6, x_6 will listen to a song or x_6 is not an office clerk we can infer that for all x_6, if x_6 were an office clerk, then x_6 is listening to a song. From the fact that for all x_6, if x_6 were an office clerk, then x_6 is listening to a song, and that for all x_6, x_6 will not listen to a song we can infer that for all x_6, x_6 is not an office clerk. Finally, from the fact that there is at least one x_6 for which x_6 is happy if and only if x_6 is an office clerk, and that for all x_6, x_6 is not an office clerk we can infer that there is at least one x_6 for which x_6 is not happy. Therefore, the answer is yes.