# Symbols for symmetric difference

I have the problem with a symbol for symmetric difference (see http://en.wikipedia.org/wiki/Symmetric_difference). In commonly used is

\triangle
\ominus


But in Polish tradition often is used:

\dot{-}


and I would like to ask if it is possible to make dot be a little bit down to (close to) line (here where is the red dot).

I've shifted the dot down 3pt relative to \dot{-}. You may adjust the value of \dysym to suit.

\documentclass{article}
\usepackage{stackengine}
\def\stacktype{L}
\stackMath
\def\dysym{-3pt}
\newcommand\symdif{\mathrel{\stackon[\dysym]{-}{\dot{\phantom{-}}}}}
\begin{document}
$$A \symdif B$$
\end{document}


If there is a need to have it work in \scriptstyle math as well, this slightly more complex version would probably be OK. By specifying \dysym in a scalable unit (ex's vs. pts), it allows spacing to (sort of) be preserved at smaller scale.

\documentclass{article}
\usepackage{stackengine}
\usepackage{scalerel}% IF YOU NEED IT FOR SCRIPTSTYLE MATH
\def\stacktype{L}
\stackMath
\def\dysym{.2ex}
\newcommand\symdif{\ThisStyle{\mathrel{%
\stackunder[\dysym]{\SavedStyle-}{\SavedStyle\dot{}}}}}
\begin{document}
$$A \symdif B$$
$$\scriptstyle A \symdif B$$
$$\scriptscriptstyle A \symdif B$$
\end{document}


• Why don’t you use a length register for \dysym, i.e. \newlength\dysym \setlength\dysym{-3pt}? – Tobi Aug 14 '13 at 19:03
• @Tobi See revision with \scriptstyle. If length register were used, the dot-dash spacing would not shrink in the smaller math style. – Steven B. Segletes Aug 14 '13 at 19:20
• @StevenB.Segletes -- well, i've tried out what i was suggesting, and you're correct -- it doesn't work. i retract (and have removed) my comment. (but i still feel there's a less complex way; i'll experiment.) – barbara beeton Aug 14 '13 at 20:36

The main problem is that the minus sign has usually the same height as the plus sign. With \ooalign one can avoid this problem:

\documentclass{article}
\providecommand{\dotminus}{\mathbin{\mathpalette\xdotminus\relax}}
\newcommand{\xdotminus}[2]{%
\ooalign{\hidewidth$\vcenter{\hbox{$#1\dot{}$}}$\hidewidth\cr$#1-$\cr}%
}

\begin{document}
$A\dotminus B$
\end{document}


I use \providecommand because at least one package (MnSymbol) defines it; but it's not advisable to load the package, that changes all math symbols.