Consider the following premises. If John writes a letter, then William is a politician. For all z, z is a soldier if and only if z will write a letter. If William were a politician, then John is a soldier. Can we infer the following from them? If we can, name the inference rule being used: If John writes a letter, then John is a soldier.
 From the fact that for all z, z is a soldier if and only if z will write a letter we can infer that John is a soldier if and only if John is writing a letter via universal instantiation. Finally, from the fact that if John writes a letter, then William is a politician, and that if William were a politician, then John is a soldier we can infer that if John writes a letter, then John is a soldier via transitivity. Therefore, the answer is yes.