http://www.math.harvard.edu/~mazur/preprints/when_is_one.pdf http://www.math.harvard.edu/~mazur/preprints/when_is_one.pdf "When is one thing equal to some othe

http://www.math.harvard.edu/~mazur/preprints/when_is_one.pdf http://www.math.harvard.edu/~mazur/preprints/when_is_one.pdf "When is one thing equal to some other thing", by Mazur