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A rotor is a convex figure that can be rotated inside a polygon (or polyhedron ) while always touching every side (or face). The least area rotor in a square is the Reuleaux triangle . The least area rotor in an equilateral triangle is a lens with two
There are many unsolved problems in mathematics. Some prominent outstanding unsolved problems (as well as some which are not necessarily so well known) include 1. The Goldbach conjecture . 2. The Riemann hypothesis .