UpDownArrow 
UpDownArrow[x,y,…]
displays as x↕y↕….
Details

- UpDownArrow[x,y,…] has no built-in meaning.
- x↕y is by default interpreted as UpDownArrow[x,y].
- ↕ can be entered as \[UpDownArrow].
Examples
Basic Examples (1)
Wolfram Research (1996), UpDownArrow, Wolfram Language function, https://reference.wolfram.com/language/ref/UpDownArrow.html.
Text
Wolfram Research (1996), UpDownArrow, Wolfram Language function, https://reference.wolfram.com/language/ref/UpDownArrow.html.
CMS
Wolfram Language. 1996. "UpDownArrow." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/UpDownArrow.html.
APA
Wolfram Language. (1996). UpDownArrow. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/UpDownArrow.html