QUOTE : In Steven Spielberg’s film Lincoln, the screenwriter Tony Kushner has the great emancipator explain Euclid’s axiom in the context of a discussion on the equality of the races: “Euclid’s first common notion is this: Things which are equal to the same thing are equal to each other. That’s a rule of mathematical reasoning. It’s true because it works. Has done and always will do. In his book Euclid says this is self-evident. You see, there it is, even in that 2,000-year-old book of mechanical law it is a self-evident truth.” Although Lincoln never actually uttered those words, there is every reason to think that he would have made just such an argument because it’s precisely what is implied in his 1854 argument that A is interchangeable with B.