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The symbol for modularly congruent is ≡, which can be produced with \equiv.

For instance,

18 ≡ 0 (mod 9)

What is the symbol for not modularly congruent, and how do I represent it in TeX?

I have perused some references (including this one) and have not found it.

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  • 8
    Is there something wrong with \not\equiv?
    – Alan Munn
    Commented Jan 30, 2012 at 3:07
  • That looks right. Thank you! In general, does \not negate the following operation?
    – David Faux
    Commented Jan 30, 2012 at 3:12
  • 1
    Yes, \not is defined zero width relation character in TeX so it will always be on top of the following character.
    – Alan Munn
    Commented Jan 30, 2012 at 3:22

2 Answers 2

66

Negation of symbols in LaTeX is typically achieved prepending it with \not. For example

Negating symbols

\documentclass{article}
\begin{document}
$18 \equiv 0\ (\textrm{mod}\ 9) \not\equiv 2\ (\textrm{mod}\ 9)$
\end{document}

For more elaborate, larger or lengthy symbols, you can use the cancel package. In those instances \not may not provide a sufficiently-centred negation. The centernot package also provides a centred \not for symbols with larger horizontal dimension.

The ≢ character is in Unicode as U+2262, and can be entered directly with unicode-math. The command for it is \nequiv in many packages, including unicode-math, pxfonts, txfonts, newpxmath, newtxmath, stix, stix2, mnsymbol and fdsymbol.

Other symbol-lookup techniques are described in How to look up a symbol or identify a math symbol or character?

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  • There's also the centernot package, which provides a \centernot command that measures its argument and centres the not correctly.
    – Alan Munn
    Commented Jan 30, 2012 at 3:39
  • 9
    Also instead of writing (\textrm{mod}\ 9), you can just write \pmod{9}. Commented Jan 19, 2014 at 4:12
  • @BlackSheep Thanks! It was annoying me that \mod creates a wide space to the left (presumably meant for when you're not using the brackets) and I found myself having to use \textrm{mod} as a workaround. So \pmod is what I was looking for!
    – Stewart
    Commented Jan 8, 2019 at 22:43
11

Here is an alternative, late answer using https://ctan.org/pkg/unicode-math, hence it requires LuaLaTeX or XeLaTeX. The example uses various modulo macros of the package amsmath.

\documentclass{memoir}
\usepackage{fontspec,amsmath,unicode-math}

\begin{document}
Here's to you, Donald and Leslie; 
\begin{align*}
    18 & \equiv 0 \bmod 9, \\
    18 &\nequiv 1  \mod 9, \\
    18 & \equiv 0 \pmod 9, \\
    18 &\nequiv 1  \pod 9.
\end{align*}
\end{document}

enter image description here

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