\cdbproperty{GammaMatrix}{\it metric={\sf metric name}}

A generalised generator of a Clifford algebra. With one vector index,
  it satisfies
\begin{equation}
\{ \Gamma^m, \Gamma^n \} = 2\,\eta^{mn}\,.
\end{equation}
The objects with more vector indices are defined as
\begin{equation}
\Gamma^{m_1\ldots m_n} = \Gamma^{[m_1}\cdots \Gamma^{m_n]}\,,
\end{equation}
where the anti-symmetrisation includes a division by~$n!$.
If you intend to use the \subscommand{join} algorithm, you have to add a
key/value pair \verb|metric| to set the name of the tensor which acts
as the unit element in the Clifford algebra.
