Torus(redirected from Toral automorphism)
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a geometric solid formed by the rotation of a circle about a line lying in the plane of the circle but not intersecting the circle (see Figure 1). A torus is shaped approximately like a doughnut or a life ring. If the radius of the rotating circle is r and
the distance from the center of the circle to the axis of rotation is a, then the area of the surface of the torus is 4π2ar and the volume of the torus is 2π2ar2. The term “torus” is also applied to the surface bounding such a solid.