I have to underbrace multiple lines in an align-environment with one brace. Meaning something like
\begin{align*}
A ={}& B + \underbracemultiline{C + D + E \\
& + F + G \\
& + H + I \\
& + J + K}_{=:M} + L
\end{align*}
results in (a nice version of)
http://www.phoenixes.de/Bsp.png http://www.phoenixes.de/Bsp.png
Another possible syntax would be
\begin{align*}
A ={}& B + \under{brace}{line}{dots}{C + D + E} \\
& \under{dots}{brace}{dots}{+ F + G}_{=:M} \\
& \under{dots}{line}{dots}{+ H + I} \\
& \under{dots}{line}{brace}{+ J + K} + L
\end{align*}
where the macro
\under{begin}{middle}{end}{What to under"line"}
is as needed for the example. How can I do this?
Thx