I want an align* environment with two columns, to display two equality signs per line, both aligned to the corresponding equality signs in the other lines.
For example:
\begin{align*}
a &= 1 + 2 + 3 &= 6 \\
b &= 1 + 2 &= 3
\end{align*}
However, when I try this in LaTeX, I get the following output:

I'd like to avoid the large space in front of =6 and =3. Does anybody know what is wrong with my code? I extracted the syntax from wikibooks.org. I also tried to add an additional & in the middle, but the result stays the same for me:
\begin{align*}
a &= 1 + 2 + 3 & &= 6 \\
b &= 1 + 2 & &= 3
\end{align*}

gather*, remove all&and it'll be ok. – yo' Mar 12 '15 at 13:59