Like multline, the split environment is for single equations that are too long to fit on one line and hence must be split into multiple lines. Unlike multline, however, the split environment provides for alignment among the split lines, using |&| to mark alignment points, as usual. In addition, unlike the other amsmath equation structures, the split environment provides no numbering, because it is intended to be used only inside some other displayed equation structure, usually an equation, align, or gather environment, which provides the numbering. For example:
\begin{equation}\label{e:barwq}\begin{split}
H_c&=\frac{1}{2n} \sum^n_{l=0}(-1)^{l}(n-{l})^{p-2}
\sum_{l _1+\dots+ l _p=l}\prod^p_{i=1} \binom{n_i}{l _i}\\
&\quad\cdot[(n-l )-(n_i-l _i)]^{n_i-l _i}\cdot
\Bigl[(n-l )^2-\sum^p_{j=1}(n_i-l _i)^2\Bigr].
\end{split}\end{equation}