Literal
Since Version 3.0 (released in 1996), Literal has been superseded by HoldPattern.
Wolfram Research (1988), Literal, Wolfram Language function, https://reference.wolfram.com/language/ref/Literal.html.
Text
Wolfram Research (1988), Literal, Wolfram Language function, https://reference.wolfram.com/language/ref/Literal.html.
CMS
Wolfram Language. 1988. "Literal." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/Literal.html.
APA
Wolfram Language. (1988). Literal. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Literal.html