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Can someone kindly explain why is there and what is the use of the ` in \catcode`@=11?

I came across that while I'm learning TeX from The TeXbook.

Thank you very much.

Mico
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Guest
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  • Welcome! I'd not vote to close as duplicate as this question is better worded (for future searches) and has a good answer, but I remember this question from the early days of this site :-) – ShreevatsaR Oct 05 '19 at 21:14

1 Answers1

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The tex syntax for a numeric literal are

123 % decimal
"12A % hex
'327 % octal
`@   % character value (= 64 here)
`\@  % same as above

so 

\catcode`@=11

is the same as

\catcode 64=11

and sets the catcode of character code 64 to 11, which has the effect of making @ a letter.

David Carlisle
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