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I am looking for the symbol := and the symbol ::=

the first one means "expressed as" (e.g. a sentence A is expressed as a juxtaposition of words bcd) and the second one means "defined as", in various applications of logic and language theory. in Linux, typing := one after one (in kile or lyx) causes vertical misalignment of the characters. I expect the center point between two dots of : and the center line through the two lines of = be on the same line, but often = is positioned too high, and also the space between them is too large, and a negetive space of -0.1 em does not look good.

Anyone like to help, telling me where to find these two symbols?

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3 Answers 3

Reset to default
11 
\documentclass{article}
\usepackage{mathtools}

\begin{document}

\[
\coloneqq\quad\Coloneqq
\]

\end{document}

enter image description here

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  • ah, i did not know of the mathtools package.
    – Sean
    Jul 24, 2013 at 14:44
4

As indicated in the The Comprehensive LaTeX Symbol List at page 31 these symbols can also be obtained in this way (without include new packages)

\mathrel{\mathop:}= enter image description here

\mathrel{\mathop:\mathop:}= enter image description here

for the second add a negative \hspace to have the symbol more condensed:

\mathrel{\mathop:\hspace{-.2em}\mathop:}=

enter image description here

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  • 1
    I'd say \mathrel{\mathop:}\mathrel{\mathop:}= because TeX inserts no space between consecutive relation symbols; or \mathrel{\mathop:\!\mathop:}= because TeX inserts a thin space between consecutive operators (no need to guess the exact amount).
    – egreg
    Jul 24, 2013 at 14:59
  • @egreg I know it's almost 4 years now, but does \mathrel{:=} do the job? (for the first symbol).
    – Pedro Sánchez Terraf
    Feb 7, 2017 at 21:03
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    @PedroSánchezTerraf No; you need \mathrel{:}= or the spacing would be wrong; on the other hand the colon will be misaligned.
    – egreg
    Feb 7, 2017 at 21:06
  • @egreg Thanks, I'll rollback to the previous suggestion; though I couldn't manage to see the difference at a glance.
    – Pedro Sánchez Terraf
    Feb 8, 2017 at 14:22
2

You can make these symbols using txfonts/pxfonts package:

\documentclass{article}
\usepackage{txfonts}
\begin{document}
$\coloneqq \Coloneqq$
\end{document}

Note: Also try loading texdoc symbols-a4 in command-line for list of symbols.

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  • this is what i was looking for : these symbols in math mode
    – Sean
    Jul 24, 2013 at 14:43
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    Usual comment: this changes all the appearance of the document. Anyway, it's better \usepackage{newtxtext,newtxmath}, because these two packages cure some shortcomings of txfonts.
    – egreg
    Jul 24, 2013 at 15:01

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