Null-A is probably the Van Vogt's most famous book, but others are great as well, I loved "Slan" from the same author : https://en.wikipedia.org/wiki/Slan https

Null-A is probably the Van Vogt's most famous book, but others are great as well, I loved "Slan" from the same author : https://en.wikipedia.org/wiki/Slan https://en.wikipedia.org/wiki/Slan