If your brain is feeling flabby, and needs a really good work-out, this is the one for you:
Godel, Escher, Bach: An Eternal Golden Braid by Douglas R. Hofstadter.
http://www.amazon.com/Godel-Escher-B.../dp/0465026567
If your brain is feeling flabby, and needs a really good work-out, this is the one for you:
Godel, Escher, Bach: An Eternal Golden Braid by Douglas R. Hofstadter.
http://www.amazon.com/Godel-Escher-B.../dp/0465026567