Reply To: Stuff to do while you wait (with a message from Harry added)
The problem is that I don’t think we can even be sure that the repetition guarantees that they are parsed to the same characters. It could just be the case that the beginning of one of the blocks extends one character before and then you end up parsing the repeated parts completely differently. This is probably not the case for this repetition and the repetition most likely corresponds to repetition in the plain text, but we can’t be sure. In the general case repetitions not at the end of the text are annoying because we don’t know where the code word ends (the code words for either repetition could extend for more characters past the repeated section). The whole problem seems very NPish and its not like we can find decent approximate solutions by starting with a random code and then hill climbing to a better answer because a random modification won’t necessarily be prefix-free.
I can also see no way forward, and if madness (or someone who has had more luck/skill with this than me) would like to give further advice that would be most appreciated.