For 10 points, name this mathematical figure that looks like a doughnut.
The fibers over a circle of latitude on S-2 forms one of these objects in S-3. The KAM theorem states that integrable Hamiltonian systems are confined to the surface of these objects. The surface area of these objects is given as 4 pi-squared times big R times little r. It takes (*) seven colors to completely color one of these objects, which can be formed by the Cartesian product of two circles. These objects have a genus of one and Euler characteristic of zero. For 10 points, name this mathematical figure that looks like a doughnut.
The fibers over a circle of latitude on S-2 forms one of these objects in S-3.
torus