A.E. van Vogt
The Golden-Age Science Fiction Author
One of van Vogt's most famous novels, The World of Null-A has appeared in three different versions over the years — the original 1945 magazine serial, the 1948 hardback book edition, and the 1970 paperback.
In early 2003 I released a PDF booklet entitled The Three Worlds of Null-A, a non-fiction study of the three different versions of the novel, with special emphasis on the many plot differences. (The sequels to this novel are not covered in this study — The Players of Null-A [aka The Pawns of Null-A], Null-A Three, and Null-A Continuum.)
I'm currently in the process of converting the old The Three Worlds of Null-A booklet into HTML, which is a long and difficult process due to the complex parallel columns and color-coding format. In the meantime, the original PDF (full of outdated links) is still available for download.