ALFRED CLEBSCH Rudolf Friedrich Alfred Clebsch (19 January 1833—7 November 1872) was a German mathematician who worked with algebraic geometry and invariant theory. He collaborated with Paul Gordan on Clebsch—Gordan coefficients for spherical harmonics, which are now widely used in quantum mechanics.The Clebsch diagonal cubic surface, or Klein's icosahedral cubic surface is a cubic surface is a well known form, all of whose 27 exceptional lines can be defined over the real numbers.