\cdbalgorithm{combine}{}

Combine two consecutive objects with indexbrackets and consecutive
contracted indices into one object with an indexbracket. An example
with two contracted matrices:
\begin{screen}{1,2}
(\Gamma_r)_{\alpha\beta} (\Gamma_{s t u})_{\beta\gamma};
@combine!(%);
(\Gamma_r \Gamma_{s t u})_{\alpha\gamma};
\end{screen}
An example with a matrix and a vector:
\begin{screen}{1,2}
(\Gamma_r)_{\alpha\beta} v_{\beta};
@combine!(%);
(\Gamma_{r} v)_{\alpha};
\end{screen}
The inverse is done by \subscommand{expand}.

\cdbseealgo{expand}
