![](https://image.tmdb.org/t/p/w500/vjVOm2CbNwwAMZMVQ5eBQM3YMN6.jpg)
A circle is also a triangle and a triangle is a square. Sound impossible? Not in the realm of topology, which even applies to 3-dimensional spaces and anything from donuts, UFOs and potatoes. The discipline's inventor, Henri Poincaré, created one of the most difficult problems in mathematics.
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