PauliChainFactor[exp] factors out all expressions inside
a PauliChain to which the chain doesn’t apply. For example,
all objects that are not Pauli matrices can be safely factored out from
every Pauli chain.
Overview, PauliChain, PCHN, PauliIndex, PauliIndexDelta, DIDelta, PauliChainJoin, PauliChainCombine, PauliChainExpand.
PCHN[CV[p, \[Nu]] CSI[a] . CSI[b] . CSI[a], i, j]
PauliChainFactor[%]\left(\overline{p}^{\nu } \overline{\sigma }^a.\overline{\sigma }^b.\overline{\sigma }^a\right){}_{ij}
\overline{p}^{\nu } \left(\overline{\sigma }^a.\overline{\sigma }^b.\overline{\sigma }^a\right){}_{ij}