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They are mathematical oddities such as the Mobius strip.
It's called a mobius strip.
A mobius strip has only two sides. As for the general name for such a class of shapes there is none.
A line (2D), ray (2D), vector (2D), line segment (2D), a mobius strip (3D), or a klein bottle (3D).
mobius strip
One can make a mobius strip very easily. First, cut a long strip of paper. Then tape the ends together in such a fashion as to create a mobius strip. If you simply tape the ends together normally, you will get a cylinder-shape. There would be two sides: one on the inside, and one on the outside. If you tape the ends together by flipping one end over (or giving it a half twist), you will get a shape that looks almost warped. On this shape, use a pencil to pinpoint a starting place. Then draw a line following the curves of the mobius strip. If the mobius strip has been made correctly, you will get back to your starting place. This is because the mobius strip is a one sided band.
He invented the Mobius Strip The Mobius Strip is a one sided surface. It is made my twisting a strip of paper and taping the two ends together.
The mobius strip was created in 1858 independently by August Fernandid Mobius and Johann Benedict Listing, two German mathematicans.
You will still have a mobius strip.
It was a mistake in the image placed there.
Karl Friedrich Gauss
According to www.answers.com, a mobius strip is a continuous one-sided surface that can be formed from a rectangular strip by rotating one end 180° and attaching it to the other end.
A Mobius strip.
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The mobius strip.