In Angola, the Chokwe people draw lines in the sand, and it's what the German mathematician Euler called a graph; we now call it an Eulerian path -- you can never lift your stylus from the surface and you can never go over the same line twice.
在安哥拉，Chokwe人在沙中绘制图线， 而这就是德国数学家欧拉称作“图”的东西。 现在，我们称之为欧拉路径--- 你的笔尖始终不能离开纸平面， 并且不能穿过同一条线两次。