LongLeftRightArrow 
LongLeftRightArrow[x,y,…]
displays as .
Details

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