# Obsolete command \Bbb

A warning keeps popping up in my LaTeX editor, and it's really annoying. It says that the command \Bbb is obsolete and I should use \mathbb instead. I personally like the command \Bbb by the obvious reason that its shorter than the newer one. If the command \Bbb is obsolete then why don't they take it out? If I try to make a new command to redefine \Bbb as \mathbb, the compiler won't let me. Is there a way to get rid of this warning?

• \let\Bbb\mathbb works for me. – Werner Apr 11 '12 at 13:19
• Also \renewcommand{\Bbb}{\mathbb} should. :) – egreg Apr 11 '12 at 13:20
• Ok. Thank you very much. I didn't know those commands. All I tried was \newcommand – Beni Bogosel Apr 11 '12 at 14:47

Since some years the command \Bbb provided by amsfonts has been renamed to \mathbb to conform to the other font selection commands (\mathcal, \mathbf and so on).

The command \Bbb has so been redefined to give a warning at the first usage, but then it works exactly as \mathbb.

Of course you're free to redefine it as you please:

\usepackage{amssymb} % or amsfonts
\renewcommand{\Bbb}{\mathbb}


In this way you'll not get any warning.

Why hasn't it been removed? Because many legacy documents use it.

• As for the way: In other words, backwards compatibility... This enables users to recompile documents written decades ago. – Dror Apr 11 '12 at 14:41

I suspect you are using this command all over the place to typeset something like a matrix or perhaps a set of numbers. You should try to separate style from content, while at the same time save your fingers from excessive typing.

\newcommand{\set}[1]{\mathbb{#1}}
...
$x \in \set{N}$


Both short and readable, and, if ever necessary, simple to change styling (e.g. you wish to use some other font for sets).