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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 http://web.ift.uib.no/Teori/KURS/WRK/TeX/symALL.html and have not found it.

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

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

Negating symbols

$18 \equiv 0\ (\textrm{mod}\ 9) \not\equiv 2\ (\textrm{mod}\ 9)$

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.

Other symbol-lookup techniques are described in How to look up a symbol?

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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 Jan 30 '12 at 3:39
Also instead of writing (\textrm{mod}\ 9), you can just write \pmod{9}. – BlackSheep Jan 19 '14 at 4:12

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