# Definition:Codomain (Set Theory)/Mapping

## Contents

## Definition

Let $f: S \to T$ be a mapping.

The **codomain** of $f$ is the set $T$.

It can be denoted $\operatorname{Cdm} \left({f}\right)$ or $\operatorname{Cod} \left({f}\right)$.

## Also known as

Some sources, for example 1975: T.S. Blyth: *Set Theory and Abstract Algebra*, also refer to the **codomain** as the **arrival set**.

On rare occasions, the **codomain** is referred to as the **target**.

Some sources write **codomain** as **co-domain**.

## A note on terminology

Some sources refer to the codomain of a mapping as its range.

However, other sources equate the term range with the image set.

Other sources brush the question aside by refraining from giving the codomain a name at all^{[1]}.

As there exists significant ambiguity as to whether the range is to mean the codomain or image set, it is advised that the term range is not used.

The notation $\operatorname{Cdm} \left({f}\right)$ has not actually been found by this author anywhere in the literature. In fact, except in the field of category theory, no symbol for the concept of codomain *has* been found, despite extensive searching.

However, using $\operatorname{Cdm}$ to mean **codomain** is a useful enough shorthand to be worth coining. That is the approach which has been taken on this website.

## Also see

## Notes and References

- ↑ 1975: W.A. Sutherland:
*Introduction to Metric and Topological Spaces*: Notation and Terminology:*A map or function (the terms are used interchangeably) between sets $A, B$ is written $f: A \to B$. We call $A$ the domain of $f$, and we avoid calling $B$ anything.*

## Sources

- 1962: Bert Mendelson:
*Introduction to Topology*... (previous) ... (next): $\S 1.6$: Functions - 1967: George McCarty:
*Topology: An Introduction with Application to Topological Groups*... (previous) ... (next): $\text{I}$: Functions - 1972: A.G. Howson:
*A Handbook of Terms used in Algebra and Analysis*... (previous) ... (next): $\S 2$: Sets and functions: Graphs and functions - 1975: T.S. Blyth:
*Set Theory and Abstract Algebra*... (previous) ... (next): $\S 4$ - 1978: Thomas A. Whitelaw:
*An Introduction to Abstract Algebra*... (previous) ... (next): $\S 20$ - 1996: H. Jerome Keisler and Joel Robbin:
*Mathematical Logic and Computability*... (previous) ... (next): Appendix $\text{A}.3$: Functions - 2000: James R. Munkres:
*Topology*(2nd ed.) ... (previous) ... (next): $1$: Set Theory and Logic: $\S 2$: Functions - 2008: David Joyner:
*Adventures in Group Theory*(2nd ed.) ... (previous) ... (next): $\S 2.1$: Functions: Definition $2.1.1$