## Quick Reference

The set of complex numbers with a point at infinity. The set can be denoted by **C**∞ and can be thought of as a Riemann sphere by means of a stereographic projection. If a sphere is placed so that a point *S* on the sphere is touching the complex plane at the origin, then *S* corresponds to the point (0,0) on the complex plane, which is the complex number *z*=0. All other points on the sphere, except *N* which is diametrically opposite to *S* on the sphere, are in a one-to-one correspondence with points on the complex plane through the stereographic projection, and therefore with a unique complex number. The point *N* is identified with the point at infinity, with corresponding complex number ∞.

*Subjects:*
Mathematics.