Consider the following premises. For all x_4, x_4 is a doctor or x_4 is not a sailor. For all x_4, x_4 will play tennis or x_4 is a sailor. For all x_4, x_4 will not play tennis. Can we infer the following from them? There is at least one x_4 for which x_4 is not a doctor.
 From the fact that for all x_4, x_4 is a doctor or x_4 is not a sailor we can infer that for all x_4, if x_4 were a sailor, then x_4 is a doctor. From the fact that for all x_4, x_4 will play tennis or x_4 is a sailor, and that for all x_4, x_4 will not play tennis we can infer that for all x_4, x_4 is a sailor. Finally, from the fact that for all x_4, if x_4 were a sailor, then x_4 is a doctor, and that for all x_4, x_4 is a sailor we can infer that for all x_4, x_4 is a doctor, which contradicts that There is at least one x_4 for which x_4 is not a doctor. Therefore, the answer is no.