2D geometrical elements and operations
xieite ::intersection2d ()
xieite ::is_linear2d <>
xieite ::line2d {}
xieite ::point2d {}
xieite ::polygon2d {}
xieite ::ray2d {}
xieite ::reflect2d ()
xieite ::rotate2d ()
xieite ::scale2d ()
xieite ::segment2d {}
xieite ::translate2d ()