Coxeter decompositions of hyperbolic polygons the sum of the angles of a hyperbolic triangle is less than 180 degrees. Coxeter decompositions are named after Harold Scott MacDonald Coxeter, an accomplished 20th century geometer. He introduced the Coxeter group, an abstract group generated by reflections. These groups have many uses, including producing the rotations of Platonic solids and tessellating the plane. Given a polygon "P", a group "G" can be generated by reflecting "P" around its sides. If the angles of "P" are /"k" for natural numbers "k", then "G" will be discrete. A Coxeter decomposition of a polygon is a decomposition into a finite number
Facial Angles (Camper) for Philipp von Stosch's "Pierres Antiques Gravées". The facial angles of Moors and Kalmyks was calculated to be 70 degrees, and that of a European 80 degrees. The original report of these lectures in the proceedings of the literature society is listed as one of the 1000 most important texts in the Canon of Dutch Literature. Facial Angles (Camper) Facial Angles refers to the content of two lectures on this subject by the Amsterdam professor of anatomy Petrus Camper on the 1st and 8 August in 1770 to the Amsterdam Drawing Academy called the "Teken-akademie". Camper was a competent artist