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