DiracChainExpand[exp] expands all Dirac chains with
explicit indices using linearity,
e.g. DCHN[GA[p1]+GA[p2]+m,i,j] becomes
DCHN[GA[p1],i,j]+DCHN[GA[p2],i,j]+m*DCHN[1,i,j].
Overview, DiracChain, DCHN, DiracIndex, DiracIndexDelta, DIDelta, DiracChainJoin, DiracChainCombine, DiracChainFactor.
DCHN[(GS[p] + m) . GA[mu], i, j]
DiracChainExpand[%]\left(\left(\bar{\gamma }\cdot \overline{p}+m\right).\bar{\gamma }^{\text{mu}}\right){}_{ij}
m \left(\bar{\gamma }^{\text{mu}}\right){}_{ij}+\left(\left(\bar{\gamma }\cdot \overline{p}\right).\bar{\gamma }^{\text{mu}}\right){}_{ij}