Put four at four conners, one at the center. Sew them up to form a rectangle. Take one end of the rectangle, turn it around (180°), and sew it up with the opposite side, to form a Mobius Band. (Is this allowed? Some kind of 3d formation is probably needed. I could not do it on a 2d plane. ) |
it is easy to paint 5 colors adjoining each other on the surface of a bike tube,but I am afraid that no one can do it on a plane.(is four color theorem proved?) |
Some people think the theorem is proven, some mathematicians do not. Recently I read from somewhere that one group proposed a much simpler human-readable proof. As for this problem, it can not be done on a plane because K_5 is not a planar graph. |
I did not realize that was the 4 color problem. (Where was my brain? ) |
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