I am reading through Kiselev's Geometry: Book I. It is a plane geometry textbook and in the introduction it says the following "One can superimpose a plane on itself or any other plane in a way that takes one given point to any other given point, and this can also be done after flipping the plane upside down" Can anyone clarify what the part in bold means, or is saying? For some background, here are some definitions given in the text The part of space occupied by a physical object is called a geometric solid. A geometric solid is seperated from the surrounding space by a surface. The flat surface is the plane.