# Double braces in equation

I'm trying to create the attached image formulae. But I don't know how to get the double braces to work. This is my attempt with only single brace.

x(t_n) = \left\{ \begin{array}{l l}
0      &\quad \mbox{ $n<ns$ or $n>ne$} \\
x(t_n) &\quad \mbox{ $ns\leq n\leq ne$}
\end{array} \right.

Could someone help me with the second brace? Thanks in advance

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This is easier to do with the cases environment than with array. Where did the image come from? –  Charles Stewart Apr 8 '11 at 14:11
I did the image in equation editor in MS Word. –  Dan Apr 8 '11 at 14:17

$$x(t_n) = \begin{cases} 0 \\ x(t_n) \end{cases} \xi(t_n) = \begin{cases} 0 &n<ns, n>ne \\ \xi(t_n) &ns\leq n\leq ne \end{cases}$$
$x(t_n) =\begin{cases} 0\\x(t_n) \end{cases}\quad \xi(t_n)=\begin{cases} 0 & \qquad\qquad (n<ns, n>ne) \\ \xi(t_n) & \qquad\qquad (n\leq n\leq ne) \end{cases}$