"Pythagoras remarked, we think, that 9+16=25. When he made this under all circumstances interesting remark, he already knew, no matter from which source, the experienced fact that a right angle is constructed by assuming the measure numbers 3, 4, 5 for the lengths of the two legs and for the distance of the end points of the same. We have pointed out that the Egyptians and the Babylonians perhaps possessed the same knowledge that the Chinese certainly had (Cantor 1880: 153)"