NotExists 
NotExists[x,y]
displays as .
Details

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