My favorite one is Russel's Paradox[1], which actually became the proof that there is no such thing as the Set of all Sets (under traditional set theory[2]). W

My favorite one is Russel's Paradox[1], which actually became the proof that there is no such thing as the Set of all Sets (under traditional set theory[2]). Which was one of my first steps into Category Theory, as Set is a proper category[3]. [1] https://en.wikipedia.org/wiki/Russell%27s_paradox https://en.wikipedia.org/wiki/Russell%27s_paradox [2] https://en.wikipedia.org/wiki/Zermelo%E2%80%93Fraenkel_set_theory https://en.wikipedia.org/wiki/Zermelo%E2%80%93Fraenkel_set_t... [3] http://en.wikipedia.org/wiki/Category_of_sets http://en.wikipedia.org/wiki/Category_of_sets