Consider the following premises. For all x_6, if x_6 drinks water, then x_6 is a sailor. There is at least one x_6 for which if x_6 works, then x_6 is drinking water. For all x_6, if x_6 works, then x_6 is a sailor. For all x_6, if x_6 were a sailor, then x_6 is working. Can we infer the following from them? For all x_6, if is not true that x_6 is a sailor if and only if x_6 will work.
 From the fact that there is at least one x_6 for which if x_6 works, then x_6 is drinking water, and that for all x_6, if x_6 drinks water, then x_6 is a sailor we can infer that there is at least one x_6 for which if x_6 works, then x_6 is a sailor. Finally, from the fact that for all x_6, if x_6 were a sailor, then x_6 is working, and that for all x_6, if x_6 works, then x_6 is a sailor we can infer that for all x_6, x_6 is a sailor if and only if x_6 will work, which contradicts that For all x_6, if is not true that x_6 is a sailor if and only if x_6 will work. Therefore, the answer is no.