# Definition:Riemann Sphere

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## Contents

## Definition

Let $f_1: \C \to \R^2$ be defined as:

- $\forall z \in \C: \map {f_1} z = \tuple {\map \Re z, \map \Im z}$

Let $f_2: \R^2 \to \R^3$ be the inclusion map:

- $\forall \tuple {a, b} \in \C^2: \map {f_2} {a, b} = \tuple {a, b, 0}$

Let $f = f_2 \circ f_1$.

Let $F: \C \to \map {\PP} {\R^3}$ be defined as the mapping which takes $z$ to the closed line interval from $\tuple {0, 0, 1}$ to $\map f z$ for all $z \in \C$.

Let $G = \set {x, y, z: x^2 + y^2 + z^2 = 1}$.

Then the Riemann map $R: \C \to \mathbb S^2$ is defined as:

- $\map R x = \map F z \cap G$

The set $R \sqbrk \C \cup \set {\tuple {0, 0, 1} } $ is called the **Riemann sphere**, with the understanding that $\map f \infty = \tuple {0, 0, 1}$.

## Also see

## Source of Name

This entry was named for Georg Friedrich Bernhard Riemann.

## Sources

- 1981: Murray R. Spiegel:
*Theory and Problems of Complex Variables*(SI ed.) ... (previous) ... (next): $1$: Complex Numbers: Spherical Representation of Complex Numbers. Stereographic Projection - 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next): Entry:**Riemann sphere**