this is the best looking edition - uses the cover art from 1945 Astounding serial.

The World of Null-A: serialized in Astounding August to October 1945 as The World of A. In the year 2650 A.D., Earth is a utopia whose leaders are selected by an omniscient Games Machine, governed by a rigid scientific policy, and seemingly forever protected from strife and war. Yet Gilbert Gosseyn faced a fact that defied all the logic of his training: standing in front of his own bullet-riddled corpse, he found himself alive in an identical body (!) ... and possessing a half-realized knowledge that offered the only hope of saving the entire Solar System from conquest by alien forces.