If I got to call substrings of Finnegans Wake when writing a computer program that generated War and Peace, I can see how that would make it shorter. Every time they shared a phrase longer than the call to Finnegans Wake, I could just call Finnegan's wake, for example. But it wouldn't save very much, I'd think.

On the other hand, a program that spat out both books could be much shorter than two programs for one book each, by some amount related to how much repetition there was.