Using the standard "align"-command, I cannot find a way to center equations between alignment characters. Is there a different environment which is better suited for this problem? My problem is as follows
\begin{align}
a &=& \underbrace{\text{insert long equation here}} &=& \text{something}\\
&=& b &=& \text{something}
\end{align}
where now the b would be displayed leftbound on the equals sign. I would like if it was displayed centered between the 2 equal signs, preferably right below the underbrace. I know that I can also add it to the underbrace, but that is not what I'm looking or.