A vertical arrow symbol serving as both a directional indicator and an extensible delimiter in mathematical expressions.
Examples
Function notation for increasing sequence
a_n \uparrow \infty \text{ as } n \to \infty
Knuth's up-arrow notation for tetration
2 \uparrow\uparrow 3 = 2^{2^2}
As a delimiter for continued fraction
\left\uparrow \frac{1}{1 + \frac{1}{2 + \frac{1}{3}}} \right\uparrow