The Möbius strip obtained by twisting one end of a rectangular piece of paper 180 degrees and gluing it to the other end is a famous example of an unorientable surface, but it is a surface with a boundary. In order to create an unorientable surface without a boundary, F. Klein came up with the idea of a surface in which two Möbius strips are glued together along their boundaries. This surface is called a Klein bottle (or tube). It can also be obtained by gluing one pair of opposite sides of a rectangle in the same direction and the other pair in the opposite direction (Figure). Source: Heibonsha World Encyclopedia, 2nd Edition Information |
長方形の紙の一方の端を180゜ねじってから他端にのり付けしたとき得られるメービウスの帯は,向きづけられない曲面として有名であるが,これは境界をもつ曲面である。そこで境界をもたない曲面で向きづけられない曲面を作るため,F.クラインは,二つのメービウスの帯をその境界に沿ってのり付けした曲面を考えた。この曲面をクラインの瓶(または管)という。これは,また,一つの長方形において1組の対辺を同じ向きに,他の組の対辺を逆の向きにのり付けすることによっても得られる(図)。
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