These are things named after Felix Klein (1849–1925), a German mathematician.
Mathematics Klein bottle Solid Klein bottle Klein configuration Klein cubic threefold Klein four-group Klein geometry Klein graphs Klein's inequality Klein model Klein polyhedron Klein surface Klein quadric Klein quartic Kleinian group Kleinian integer Kleinian model Kleinian ring Kleinian singularity Klein's icosahedral cubic surface Klein's j-invariant Beltrami–Klein model Cayley–Klein metric Clifford–Klein form Schottky–Klein prime form
Other Klein's Encyclopedia of Mathematical Sciences The Felix Klein Protocols Felix Klein medal, named after the first president of the ICMI (1908–1920), honours a lifetime achievement in mathematics education research. The Klein project of the IMU and ICMI aims to produce a book for upper secondary teachers that communicates the breadth and vitality of the research discipline of mathematics and connects it to the senior secondary school curriculum.
