# How can systems be side by side with an arrow between them

Here's my problem : I'd like to a write many equivalent systems of equations. Therefore, I'd like the first to be at the left, then an arrow (\Leftrightarrow, for example, since they're equivalent :)), a second one on the right, and then, the others vertically aligned with the second. Basically, I want to do the same thing that can be done with the align environment, but with systems. Nevertheless, I didn't figure it out.

Here's what I tried :

\documentclass[11pt]{article}
\usepackage{envmath}
\begin{document}
$\begin{System} x + y = 3 \\ x - y = 1 \end{System} \Leftrightarrow \begin{System} x=2\\ y=1 \end{System}$
\end{document}


Would you have any solution ?

• Would you have examples of these systems to start with? – percusse Mar 16 '14 at 16:48
• @Araen, you can edit your posts Although the "edit" link is a little hard to see. I've moved your comment into your post. – Thruston Mar 16 '14 at 17:00
• amsmath is better than envmath. – egreg Mar 17 '14 at 8:59

## 3 Answers

You could use aligned and \iff which produces the correct math spacing: ## Code:

\documentclass[11pt]{article}
\usepackage{amsmath}

\begin{document}
\left\{\begin{aligned} x + y &= 3 \\ x - y &= 1 \end{aligned}\right. \iff \left\{\begin{aligned} x &= 2\\ y &= 1 \end{aligned}\right.
\end{document}


Put everything in a tabular environment:

\documentclass[11pt]{article}

\begin{document}

\begin{tabular}{lll}
$\left\{\begin{tabular}{l}x+y=3 \\ x-y=1 \\ \end{tabular}\right.$ & $\Leftrightarrow$ & $\left\{\begin{tabular}{l}x=2 \\ y=1 \\ \end{tabular}\right.$ \\
& & \\
& $\Leftrightarrow$ & $\left\{\begin{tabular}{l}x=2 \\ y=1 \\ \end{tabular}\right.$ \\
\end{tabular}

\end{document} • Are you sure about tabular? Shouldn't it be array? – egreg Mar 17 '14 at 8:53

Without any package:

\documentclass{article}
\begin{document}
$\left\{\!\!\begin{array}{c} x+y=3\\ x-y=1 \end{array}\right. \!\!\Leftrightarrow \left\{\!\! \begin{array}{c} x=2\\ y=1 \end{array} \right.$
\end{document}


The negative spaces \!\! are to obtain a spacing similar to Peter's answer, but may be is OK for you with some more spacing around the brackets. This is the difference: 