[SOLVED] adding braces above a Matrix

Hi everyone!

I'm trying to add some braces above/below and left/right of a Matrix to describe how many Columns and Rows certain ranges of the matrix has.

For example I have a 2 by 2 Block-matrix. I want a brace over the first and the one over the second column telling me how large each blockmatrix is.

\overbrace doesn't seem to work for me because either the brace and it's description end up inside the matrix or the braces are over the brackets and the column to be braced.

Here's what I've tried sofar:

\[

\left[ {\begin{array}{*{20}c}

1 & 2 \\

3 & 4 \\

\end{array}} \right] + \overbrace {\left[ {\begin{array}{*{20}c}

1 \\

3 \\

\end{array}} \right.}^N\quad \overbrace {\left. {\begin{array}{*{20}c}

2 \\

4 \\

\end{array}} \right]}^k\begin{array}{*{20}c}

{\left. {} \right\}N}\\

{\left. {} \right\}k}\\

\end{array}

\]

I hope someone knows a solution to this problem.

Michael