Consider the following premises. There is at least one x_7 for which x_7 will take a plane or x_7 will climb a mountain. For all x_7, x_7 will take a plane if and only if x_7 is a sailor. For all x_7, if x_7 climbs a mountain, then x_7 is writing a letter. For all x_7, if x_7 writes a letter, then x_7 is a sailor. Can we infer the following from them? For all x_7, x_7 is not a sailor.
 From the fact that for all x_7, x_7 will take a plane if and only if x_7 is a sailor we can infer that for all x_7, if x_7 takes a plane, then x_7 is a sailor. From the fact that for all x_7, if x_7 climbs a mountain, then x_7 is writing a letter, and that for all x_7, if x_7 writes a letter, then x_7 is a sailor we can infer that for all x_7, if x_7 climbs a mountain, then x_7 is a sailor. Finally, from the fact that for all x_7, if x_7 takes a plane, then x_7 is a sailor, that for all x_7, if x_7 climbs a mountain, then x_7 is a sailor, and that there is at least one x_7 for which x_7 will take a plane or x_7 will climb a mountain we can infer that there is at least one x_7 for which x_7 is a sailor, which contradicts that For all x_7, x_7 is not a sailor. Therefore, the answer is no.