What does $\uparrow$ mean in the context?

Question

The set up is as follows: "Let $f_n, f: \mathbb{R} \rightarrow \mathbb{R}$ be functions such that $f_n \uparrow f, n \rightarrow \infty$." I know what it means that $f_n \rightarrow f, n \rightarrow \infty$, but can anyone explain the meaning when the $\uparrow$ is used?

Answer 1

$f_n \uparrow f$ means that $f_n \to f$ and $f_n$ is a monotone increasing sequence i.e. $f_{n+1}(x) \geq f_n(x)$ for every $n,x$.