This question already has an answer here:
About fifteen or twenty years ago, I read an article (online, I think) which discussed, among other things, the structure of science fiction "fix-up" novels, which are put together from pre-existing pieces of shorter fiction. Among general facts about the genre, it described some interesting specific examples.
One piece of trivia that was mentioned was that an author had actually used the same piece of short fiction in two different fix-ups! I don't remember any other details; in fact, I think there weren't really any other details given. However, it sounds like a fascinating and strange thing for any author to do. Does anybody know what the author and story invovled were? (From the context in the article, I am pretty sure it was not van Vogt, since he was identified in a different part of the article as the author who coined the term "fix-up.")