Van Vogt's earlier Null-A novels explore a philosophic, educational and analytical system advanced by Alfred Korzybski called General Semantics. The stories are interesting if more than a little off the GS mark. The third Null-A novel is a disaster. I won't go into details of plot but each of the Null-A books explores a theme. The first addressed a question of identity that remains both fresh and current. The second, well, it seems to continue that exploration, more or less, after a fashion, sort of; and it tosses in a direct contradiction to Null-A philosophy as key plot device. It still hangs interesting GS quotes at the chapter headings, but, well van Vogt tried too hard. And 3? Well in 3 it doesn't seem as if he tried at all. If anything, 3 seems to be about child rearing and education, with an attractive widow. Stick to Null-A 1 and if you must, Null-A 2.