# Definition:One (Cardinal)

Jump to navigation
Jump to search

## Definition

The cardinal associated with the singleton $\left\{{\varnothing}\right\}$ is called **one**, and is denoted $1$.

More informally, this means that **one** is defined as being **the number of elements in a singleton set**.

## Sources

- 1975: T.S. Blyth:
*Set Theory and Abstract Algebra*... (previous) ... (next): $\S 8$