A less used presentation of the Möbius strip is as the topological quotient of a torus. A torus can be constructed as the square formula_12 with the edges identified as formula_16 (glue left to right) and formula_17 (glue bottom to top). If one then also identified , then one obtains the Möbius strip. The diagonal of the square (the points where both coordinates agree) becomes the boundary of the Möbius strip, and carries an orbifold structure, which geometrically corresponds to "reflection" – geodesics (straight lines) in the Möbius strip reflect off the edge back into the strip. Notationally, this is written as T2/S2 – the 2-torus quotiented by the group action of the symmetric group on two letters (switching coordinates), and it can be thought of as the configuration space of two unordered points on the circle, possibly the same (the edge corresponds to the points being the same), with the torus corresponding to two ordered points on the circle.