Double torus

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In mathematics, a double torus is a topological object formed by the connected sum of two torii. That is to say, from each of two torii the interior of a disk is removed, and the boundaries of the two disks are identified (glued together), forming a double torus.

This is the simplest case of an n-torus, which is the connected sum of n torii. An n-torus is an example of a two dimensional manifold. According to the classification theorem for 2-manifolds, every compact connected 2-manifold is either a sphere, an n-torus, a projective plane or the connected sum of projective planes.

Double torus knots are studied in knot theory.