moebius river bands
The Möbius Band is the building block for non-orientable surfaces. It is formed by joining the ends of a rectangle with a twist (180 degrees). Any non-orientable surface contains a Möbius Band, and any surface which contains a Möbius Band is necessarily non-orientable. It is not closed--hence it is not a surface, and it contains one boundary curve. The Möbius Band cannot be embedded in the plane, R^2.
Thames & Hudson, Lockwood & Haendel, lado a lado, vertidos e invertidos, para a frente e para trás, duas vezes dois canais numa só banda. (ver 21.01.07)