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I am using WinEdt 6 for compiling my TeX documents. I am getting an error with contains the line $\mathbb{Z}$ showing that it is undefined control sequence. How should I rectify it? Should I include any math packages or something. I am a beginner in using TeX.

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    This was my very first LaTeX error! It took me days to figure out; no online resource I read thought to mention that it was assuming the amssymb package.
    – Ryan Reich
    Dec 19, 2011 at 16:19
  • tex.ac.uk/cgi-bin/texfaq2html?label=numbersets describes the AMS fonts, and says "Support files for using the fonts, both under Plain TeX and LaTeX (packages amssymb and amsfonts), are available. [...]". this of course doesn't help, if you're a person who doesn't like to read faq answers...
    – wasteofspace
    Dec 19, 2011 at 16:56
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    did you try \usepackage{amsfonts}? I don't think anything else is needed in a very basic overleaf new doc.
    – Charlie Parker
    Feb 22, 2022 at 0:24

4 Answers 4

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Load the amsfonts package, this provides that command:

\documentclass{article}
\usepackage{amsfonts}
\begin{document}
$\mathbb{Z}$
\end{document}

Optionally you could load amssymb, as this in turn loads amsfonts.

\documentclass{article}
\usepackage{amssymb}
\begin{document}
$\mathbb{Z}$
\end{document}

For reference, the Comprehensive LaTeX Symbol List has also a table of mathematical alphabets, and the packages required for using them. In the current version (dated 25 June 2020) of the document, it is table 316 with the caption Math Alphabets. It is the final table in chapter 3 Mathematical symbols.

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  • Thank you. Would the same be sufficient for \mathds??
    – Ramana Venkata
    Dec 19, 2011 at 11:03
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    @RamanaVenkata No, for that you have to load the dsfont package.
    – Torbjørn T.
    Dec 19, 2011 at 11:07
  • I guess the document you reference is subject to chance, if other people are looking for it here a description that is hopefully less prone to change. Look at the chapter called Mathematical symbols (currently chapter 3) and look for the table called "mathematical alphabets". It is last table in that chapter at this moment and currently numbered 307.
    – Maarten Derickx
    Jun 1, 2018 at 9:07
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    Apparently amsmath does not load amsfonts automatically.
    – Solomon Ucko
    Jan 25, 2019 at 20:41
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    @SolomonUcko -- Indeed, amsmath does not load amsfonts. When these packages were created, memory was at a premium, and loading of necessary packages was left to the user.
    – barbara beeton
    Jan 10, 2020 at 3:07
6

The \mathbb command is provided via the amsfonts package. Add

\usepackage{amsfonts}

to the preamble to solve this problem.

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You can load many other fonts for \mathbb with either unicode-math, which supports modern OpenType math fonts, or mathalpha, which supports legacy 8-bit math alphabets.

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  • using \usepackage{amsfonts} is easier, no?
    – Charlie Parker
    Feb 22, 2022 at 0:27
  • @CharlieParker obviously that depends on your document. If you want some other alphabets, like script and other not provided by amsfonts you will end up loading many more packages than just unicode-math. Another example when unicode-math is more useful is when you need to load many fonts (not recommended but it is possible). You have to give a try to unicode-math and decide by yourself which package is better in certain contexts.
    – Luis Turcio
    Feb 22, 2022 at 1:16
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You can use the following two packages.

\usepackage{amsmath}
\usepackage{amssymb}
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    Welcome to TSE. Your answer adds nothing new to the already existing answers.
    – José Carlos Santos
    May 22, 2022 at 14:35
  • While true that blackboard bold Z will appear if these two packages are used, only amsfonts is needed, and that is loaded automatically by amssymb.
    – barbara beeton
    May 22, 2022 at 16:31

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