 Klein advocated this view in a pamphlet published when he became a Professor at the University of Erlangen in 1872 and other publications in journals in the 1870s in order to re-unify geometry. He presented a way of showing that metrical geometries, such as Euclidean and non-Euclidean geometry, and other geometries, such as inversive geometry and birational geometry, can be regarded as special cases of projective geometry (as can affine geometry, which he did not know about in 1872).