The projective line over the dual numbers was described by Josef Grünwald in 1906. This ring includes a nonzero nilpotent "n" satisfying . The plane of dual numbers has a projective line including a line of points . Isaak Yaglom has described it as an "inversive Galilean plane" that has the topology of a cylinder when the supplementary line is included. Similarly, if "A" is a local ring, then P("A") is formed by adjoining points corresponding to the elements of the maximal ideal of "A".