DiracChainFactor[exp] factors out all expressions inside a DiracChain to which the chain doesn’t apply. For example, all objects that are not Dirac matrices can be safely factrored out from every Dirac chain.
Overview, DiracChain, DCHN, DiracIndex, DiracIndexDelta, DIDelta, DiracChainJoin, DiracChainCombine, DiracChainExpand.
DCHN[FV[p, \[Nu]] GA[\[Mu]] . GA[\[Nu]] . GA[\[Mu]], i, j]
DiracChainFactor[%]\left(\overline{p}^{\nu } \bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }.\bar{\gamma }^{\mu }\right){}_{ij}
\overline{p}^{\nu } \left(\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }.\bar{\gamma }^{\mu }\right){}_{ij}