You have most likely encountered one-sided objects hundreds of times in your daily life – like the universal symbol for recycling, found printed on the backs of aluminum cans and plastic bottles. This ...

Editor’s Note: Published in 1957, this article comes from Martin Gardner’s legendary Scientific American column Mathematical Games. Read more in our special digital issue, Fun and Games. As many ...

A Möbius strip can irritate our perception. At first sight, the strip has two sides and two edges just like a normal ring made from a strip of paper, for example. If you follow one side or one edge ...

In the field of symplectic geometry, a central issue involves how to count the intersection points of two complicated geometric spaces. This counting question is at the heart of one of the most famous ...