Let ${}T\subseteq \mathbb {R}$ denote a subset and ${}a\in \mathbb {R}$ a point. Let

- $f\colon T\longrightarrow \mathbb {R}$

be a function and ${}b\in \mathbb {R}$ a point. Show that the following statements are equivalent.

- We have
- ${}\operatorname {lim} _{x\rightarrow a}\,f(x)=b\,.$

- For every sequence ${}{\left(x_{n}\right)}_{n\in \mathbb {N} }$ in ${}T$ which converges to ${}a$, also the image sequence ${}{\left(f(x_{n})\right)}_{n\in \mathbb {N} }$ converges to ${}b$.