*sigh* Some books should remain fond memories. 
 I'm dropping a star on the re-read. Enjoying the insistence of intuitionalism doesn't make up for the abysmally uninteresting aliens or the 1970's culturally-locked ideas surrounding smart human women and smart alien women. It was actually pretty groan-worthy. 
 As for the actual story idea, I enjoyed the extrapolation of a modified natural law and the SF conversation Asimov was having with Silverberg, but it turns out that a tiny handful of ideas isn't enough to carry the novel. I'm a firm believer in truly excellent characters and story. As this novel is, it's more of a thinly-veiled science instructional tidied up with a few SF tropes and a single good Science Idea mixed with a single good cultural/mental/personal Idea. 
 I like intuition. I love it, even. Asimov does, too. Bravo. Moving on. 
 Destruction of two universes feeding off each other. Sound cool? It is. But even Lensman did it better than this. :) 
 Alas, this is NOT Asimov's best work. Foundation is much better and I had a grand lot of fun with the Robot books. This one is Far down that list, and I'm sad. I can't believe this made a Hugo. 1972 must have been a very lean year.