looking for the symbol :=

Question

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?

score 12 · Accepted Answer · answered Jul 24 '13 at 14:24

12

\documentclass{article}
\usepackage{mathtools}

\begin{document}

\[
\coloneqq\quad\Coloneqq
\]

\end{document}

enter image description here

answered Jul 24 '13 at 14:24

Gonzalo Medina

505,128

ah, i did not know of the mathtools package. – Sean Jul 24 '13 at 14:44

score 4 · Answer 2 · edited Sep 30 '22 at 23:31

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

edited Sep 30 '22 at 23:31

David Carlisle

757,742

answered Jul 24 '13 at 14:32

Red

10,181

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
@egreg I know it's almost 4 years now, but does \mathrel{:=} do the job? (for the first symbol). – Pedro Sánchez Terraf Feb 07 '17 at 21:03
1

@PedroSánchezTerraf No; you need \mathrel{:}= or the spacing would be wrong; on the other hand the colon will be misaligned. – egreg Feb 07 '17 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 08 '17 at 14:22

score 2 · Answer 3 · answered Jul 24 '13 at 14:27

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.

answered Jul 24 '13 at 14:27

Jagath

4,287

this is what i was looking for : these symbols in math mode – Sean Jul 24 '13 at 14:43
2

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

looking for the symbol :=

3 Answers3