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Marcus du Sautoy explores the classic problem of the bridges of Konigsberg: is it possible to cross its seven bridges without crossing any of them twice? Euler solved this problem by looking at it as a topological problem. It is how they are connected, rather than the distances between them, that matters. Poincare took topology and made it a very important area of Maths, and the clip explores how some shapes, like a bagel and a football, are topologically different.