I read on Wikipedia that G. Spencer-Brown gave a non-computer based proof of the four color theorem. As I'm not an expert in the subject I'm unable to verify that claim. Does any one have an idea about the proof or a reference to a serious discussion of the subject?
Post Closed as "not constructive" by Robin Chapman, Felipe Voloch, Theo Johnson-Freyd, Gerry Myerson, S. Carnahan♦