# The \bar and \overline commands

I want to represent, say, the closure of a set or the extended reals, e.g., $\bar{\mathbb{R}}$ but unfortunately this creates a bar that is much too small (horizontally) and can barely be seen. On the other hand, $\overline{\mathbb{R}}$ creates a line that is too long. I need something that's just right, in between the bar and the overline. What would be my best choice?

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See also this answer of mine for a \widebar command that produces a bar wider than \bar and smaller than \overline. – Hendrik Vogt May 13 '13 at 12:25
Related Question: Overline thickness. – Peter Grill Aug 23 '14 at 16:25

Here is a command \xoverline[width percent]{symb} that will do it. Note that it will not scale inside sub or superscripts. If you need that, everthing has to go through a \mathchoice resulting in a lot more complex code.

\documentclass{article}
\usepackage{amsmath,amssymb}
\makeatletter
\newsavebox\myboxA
\newsavebox\myboxB
\newlength\mylenA

\newcommand*\xoverline[2][0.75]{%
\sbox{\myboxA}{$\m@th#2$}%
\setbox\myboxB\null% Phantom box
\ht\myboxB=\ht\myboxA%
\dp\myboxB=\dp\myboxA%
\wd\myboxB=#1\wd\myboxA% Scale phantom
\sbox\myboxB{$\m@th\overline{\copy\myboxB}$}%  Overlined phantom
\setlength\mylenA{\the\wd\myboxA}%   calc width diff
\ifdim\wd\myboxB<\wd\myboxA%
\rlap{\hskip 0.5\mylenA\usebox\myboxB}{\usebox\myboxA}%
\else
\hskip -0.5\mylenA\rlap{\usebox\myboxA}{\hskip 0.5\mylenA\usebox\myboxB}%
\fi}
\makeatother
\begin{document}

$|\xoverline{W}|~~ |\xoverline{i}|~~ |\xoverline[3.0]{i}|$

\bigskip

$\bar{\mathbb{R}}~~\overline{\mathbb{R}}~~\xoverline{\mathbb{R}}$

\end{document}


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Wow, I never knew this would be so involved! Very nice answer though and thanks for your help. – 3Sphere Jul 2 '11 at 13:08
Someone should do the \mathchoice thing and package this into a package! – Mariano Suárez-Alvarez Jun 27 '14 at 5:38

I usually define a command \overbar, which reduced the width of \overline by 1.5mu on each side.

\documentclass{article}

\usepackage{amsfonts}

\newcommand{\overbar}[1]{\mkern 1.5mu\overline{\mkern-1.5mu#1\mkern-1.5mu}\mkern 1.5mu}

\begin{document}
$\bar{\mathbb{R}}$ $\overbar{\mathbb{R}}$ $\overline{\mathbb{R}}$
\end{document}


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