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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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1  
Welcome to TeX.SX! Usually, we don't put a greeting or a “thank you” in our posts. While this might seem strange at first, it is not a sign of lack of politeness, but rather part of our trying to keep everything very concise. Accepting and upvoting answers is the preferred way here to say “thank you” to users who helped you. –  Kurt Jul 24 '13 at 14:27
    
@kurt, i already tried detexify, it did not help. i was not familiar with the other two sources.. –  Sean Jul 24 '13 at 14:42
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marked as duplicate by Werner, lockstep, Claudio Fiandrino, Thorsten, Kurt Jul 24 '13 at 14:57

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3 Answers

up vote 5 down vote accepted
\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 '13 at 14:44
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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 '13 at 14:43
    
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 '13 at 15:01
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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 '13 at 14:59
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