Consider the following premises. There is at least one x_7 for which x_7 will work. For all x_7, x_7 will work if and only if x_7 will write a letter. For all x_7, x_7 will not write a letter. Can we infer the following from them? There is at least one x_7 for which x_7 is a police officer.
 From the fact that for all x_7, x_7 will work if and only if x_7 will write a letter, and that for all x_7, x_7 will not write a letter we can infer that for all x_7, x_7 will not work. From the fact that there is at least one x_7 for which x_7 will work we can infer that there is at least one x_7 for which x_7 will work or x_7 is a police officer. Finally, from the fact that there is at least one x_7 for which x_7 will work or x_7 is a police officer, and that for all x_7, x_7 will not work we can infer that there is at least one x_7 for which x_7 is a police officer. Therefore, the answer is yes. Notice, however, that the premises were contradictory, so we can infer anything from them.