actually held in the opposite direction opposite direction says if you have a set of length L that satisfy that same thing then there is a code you can build in fact the prefix code which is very convenient to deal with which is uniquely decodable of the same size as these links so it's a back and forth kind of mapping if something uniquely decodable this is satisfied if don't satisfy this you can build uniquely decodable code that in fact the prefix to a tree that allows you to encode symbols with feet word lengths what does