# Illustrate distributive law with “broken” arrows

I would like to obtain the following formatting.

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You could (ab-) use chemmacros's redox macros:

% arara: pdflatex
% arara: pdflatex
\documentclass{scrartcl}
\usepackage{chemmacros}

\begin{document}

$$\OX{first,k}(\OX{second,a}+\OX{third,b}) = ka + kb$$
\redox(first,second)[->]{$\times$}
\redox(first,third)[->][-1]{$\times$}

\end{document}


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Neat! Just a quick suggestion -- if you prefixed \scriptsize to the two instances of $\times$, the multiplication symbol's size would be (slightly) better proportioned. –  Mico Jun 24 '12 at 12:11
Sure, why not. I simply wanted to demonstrate the basic principle. :) –  cgnieder Jun 24 '12 at 14:30