Consider the following premises. For all x_7, x_7 will take a plane if and only if x_7 is a mechanic. For all x_7, if x_7 were an office clerk, then x_7 is a sailor. For all x_7, x_7 will not take a plane. For all x_7, x_7 is a sailor if and only if x_7 is a mechanic. Can we infer the following from them? There is at least one x_7 for which x_7 is an office clerk.
 From the fact that for all x_7, x_7 will take a plane if and only if x_7 is a mechanic, and that for all x_7, x_7 will not take a plane we can infer that for all x_7, x_7 is not a mechanic. From the fact that for all x_7, x_7 is a sailor if and only if x_7 is a mechanic, and that for all x_7, x_7 is not a mechanic we can infer that for all x_7, x_7 is not a sailor. Finally, from the fact that for all x_7, if x_7 were an office clerk, then x_7 is a sailor, and that for all x_7, x_7 is not a sailor we can infer that for all x_7, x_7 is not an office clerk, which contradicts that There is at least one x_7 for which x_7 is an office clerk. Therefore, the answer is no.