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What is the correct way to make the "does not divide" symbol in plain LaTeX 2e?

I'm talking about the symbol that is a vertical bar with a slash through it. I prefer not to install AMS or other packages, but instead to use plain LaTeX.

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6 Answers 6

90

Try this:

$x\nmid y$

It has been known to 'save the day'.

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  • That doesn't work in plain LaTeX. Do you know what package must be loaded to make it work? I tried \usepackage{amsfonts} but that doesn't work. And I still prefer a plain LaTeX solution.
    – user448810
    Aug 5, 2011 at 22:33
  • 12
    I got \nmid working with \usepackage{amssymb}.
    – user448810
    Aug 5, 2011 at 22:46
18

Detexify is amazingly helpful in finding any symbol.

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6

Using \not with | works with plain LaTeX:

\documentclass{article}
\begin{document}
$2 \not| \;3 $
\end{document}

The symbols \\, and \: and \; create varying degrees of space if the symbols get too close.

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  • I wonder why the \not introduces so much space. Jun 22, 2012 at 1:11
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    I'm not sure which space you're talking about but try this: $2 \!\!\not| \,3 $. The \! is negative space to get things closer together on the right and \, will reduce space on the right
    – DJP
    Jun 22, 2012 at 1:26
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    Oh, I didn't think you'd come back to this! Thanks very much. I just meant that while a|b is nice and compact, a\not|b puts a strange amount of space between a and |. Jun 22, 2012 at 1:28
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    I don't know why \not has so much extra space but if I had to guess it might be because \not can be used in conjunction with a lot of other symbols which are wider than | [eg \not\in or \not\subset]. So some combinations will look better than others depending on the symbol width being negated.
    – DJP
    Jun 22, 2012 at 1:48
  • The spacing on \not\mid was ok when I used it on mathoverflow (mathoverflow.net/questions/256598/…) Dec 7, 2016 at 7:41
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To minimize used packages you can do this:
\newcommand{\ndiv}{\hspace{-4pt}\not|\hspace{2pt}}
From then on \ndiv will add the sign with appropriate spaces before and after.

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  • 3
    If the font size changes, this can cause a lot of headache. At least you can opt for units like ex,em but still it would not be robust enough to be used elsewhere.
    – percusse
    Nov 27, 2012 at 1:11
  • @percusse: can you provide a more robust way?
    – cxxl
    May 23, 2013 at 8:02
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    @cxxl The answers above are pretty good. Otherwise you can look for the definitions from the LaTeX versions and carry them to plain TeX as raw macros.
    – percusse
    May 23, 2013 at 20:55
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The ∤ symbol is available in Unicode as U+2224 Does Not Divide, and as \nmid from many packages, including: unicode-math, amssymb, stix, stix2, newtxmath and the less commonly-usedmnsymbol, fdsymbol and boisk.

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After fine tuning, I'm pretty happy with defining a new command \doesnotdivide (or whatever you'd like to name it) as: \newcommand{\doesnotdivide}{\not\hspace{2.5pt}\mid}

I found that three points was too much and 2 points was not enough offset.

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    This is somewhat similar to blerbl's answer. Note that a comment there points out that measuring in em would be better than pt, since it would automatically adjust to a change in font size.
    – Teepeemm
    May 2, 2019 at 0:23

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