In 2D, the symmetry group D n includes reflections in lines. When the 2D plane is embedded horizontally in a 3D space, such a reflection can either be viewed as the restriction to that plane of a reflection through a vertical plane, or as the restriction to the plane of a rotation about the reflection line, by 180°. In 3D, the two operations are distinguished: the group D n contains rotations only, not reflections. The other group is pyramidal symmetry C nv of the same order, 2 n.