Thanks - I have to admit there's far too much jargon in there for me to make heads or tails of the main claims, let alone say anything sensible about your original reply. I can't even work out how your statement that no algorithmic process can increase the mutual information between two given strings is formalised in the language of the paper, since there seems to be an obvious counterexample - the mutual information between an infinite string of 0s and the halting sequence can be made arbitrarily large by a program with oracle access to the halting sequence by simply transforming each element into the corresponding element of the halting sequence. So of course I am missing something.

But it seems interesting, thanks for the link =)