EntityQ652123· pop 8· linked from 41 articlestriangle groupSign in to saveGroup realized geometrically by reflections across the sides of a triangleConnectionspoint reflectionEntitymodular groupEntitySchwarz triangleEntitymathematicsEntitytriangleEntityInternational Standard Book NumberEntityintegerEntitysphereEntitycubeEntitydigital object identifierEntitygroupEntityplaneEntityEuclidean geometryEntityradianEntityWilliam Rowan HamiltonEntitytetrahedronEntityrotationEntityPlatonic solidEntityAlexander GrothendieckEntitycongruenceEntityCategoriesCoxeter groupsEuclidean geometryFinite groupsGeometric group theoryHyperbolic geometryPolyhedraProperties of groupsSpherical trigonometryTessellation