# Two double-line equations need double left brackets

I have four lines of equations. The first two and the second two need to be grouped by a left bracket, and all four need to be grouped by one overall left bracket.

I am using an array within an equation. I can't manage to add the two 'inner' left brackets. The one big left bracket over all four equations is not a problem, which is the following:

\begin{equation}
\left\{
\begin{array}{lcl}
1\\
2\\
3\\
4
\end{array}
\right.
\end{equation}


And this seems to work just fine. But when I try the following

\begin{equation}
\left\{
\begin{array}{lcl}
\left\{
\begin{array}{lcl}
1\\
2
\end{array}{lcl}
\right.
\end{array}
\begin{array}{lcl}
\left\{
\begin{array}{lcl}
3\\
4
\end{array}
\right.
\end{array}
\right.
\end{equation}


it doesn't work. I've tried some other changes, including changing to eqnarray, or changing the places of the brackets, but nothing seems to work. Now I am not sure how to solve this.

I think that some information about the actual expressions might be useful to decide which structure(s) would be best to use; in its present form (using arrays for the two subgroups), one could use a cases environment for the outer brace:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation}
\begin{cases}
\left\{
\begin{array}{lcl}
1 \\
2
\end{array}
\right. \\
\left\{
\begin{array}{lcl}
3 \\
4
\end{array}
\right.
\end{cases}
\end{equation}

\end{document} Here's another option, using a gather environment for the whole structure, and nested arrays:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{gather}
\left\{
\begin{array}{@{}l@{}}
\left\{
\begin{array}{lcl}
1 \\
2
\end{array}
\right. \\
\left\{
\begin{array}{lcl}
3 \\
4
\end{array}
\right.
\end{array}
\right.
\end{gather}

\end{document} By the way, your code has some typos like \end{array{lcl}.

• Thanks, yes I typed a bit quick :-) The expressions are differential equations. So it's all pure math in there. Or would you need to know more specifically? I don't know the environments cases or gather. I'll give them a try and see how they work, thanks! – Ampi Severe Apr 18 '13 at 10:09
• They both work perfectly well :-). I like the cases environment very much, but output for both is the same. Thanks! – Ampi Severe Apr 18 '13 at 10:19