what's a replacement for \lefteqn in the align environment?

Question

I would like to avoid the use of eqnarray. I would like to use the align environment instead.

However, I have an equation that I specify currently the following way:

\begin{eqnarray}
\lefteqn{f(a,b,c,d,e,...)} \\
& = & A
\end{eqnarray}

as you can see, I am using \lefteqn, and that cannot be used in the align environment (the reason for using \lefteqn is because f(a,b,c,...) is a very long term).

Any ideas how to do that with the align environment (something corresponding to the align environment)?

EDIT:

\lefteqn helps better alignment for long equations in a certain line. Whenever you have a long term appearing in a certain line, you can use lefteqn so that the line below is not put vertically right after the long line. It is hard to perhaps explain, but the idea is that you would get something like:

 very long text =
   continue here

instead of

  very long text =
                   continue here

Answer 1

Use \MoveEqLeft from the mathtools package, like this:

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{align}
\MoveEqLeft \text{very very long} \\
 &= \text{shorter}
\end{align}
\end{document}

Edit: If you feel that this doesn't move the first line far enough to the left, then use, e.g., \MoveEqLeft[4] instead of \MoveEqLeft. This moves the first line 4em to the left; the default is 2em. See also page 17 of the mathtools documentation.

Answer 2

I prefer combining multline with aligned:

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{multline}
x=\\
\begin{aligned*}
 &= y\\
 &= z
\end{aligned*}
\end{multline}
\end{document}