DCHN[x, i, j] is a chain of Dirac matrices x and is transformed into DiracChain[FCI[x],DiracIndex[i],DiracIndex[j]] by FeynCalcInternal.
Overview, DiracChain, DCHN, DiracIndex, DiracIndexDelta, DiracChainJoin, DiracChainExpand, DiracChainFactor.
A standalone Dirac matrix with open Dirac indices
DCHN[GAD[\[Mu]], i, j]\left(\gamma ^{\mu }\right){}_{ij}
A chain of Dirac matrices with open Dirac indices
DCHN[GAD[\[Mu]] . GAD[\[Nu]], i, j]\left(\gamma ^{\mu }.\gamma ^{\nu }\right){}_{ij}
A single \bar{u} spinor with an open Dirac index
DCHN[SpinorUBar[p, m], i]\left(\bar{u}(p,m)\right)_i
A single \bar{v} spinor with an open Dirac index
DCHN[SpinorVBar[p, m], i]\left(\bar{v}(p,m)\right)_i
A single u spinor with an open Dirac index
DCHN[i, SpinorU[p, m]](u(p,m))_i
A single v spinor with an open Dirac index
DCHN[i, SpinorV[p, m]](v(p,m))_i
\bar{u} spinor contracted with a chain of Dirac matrices
DCHN[GAD[\[Mu]] . GAD[\[Nu]], SpinorUBar[p, m], j]\left(\bar{u}(p,m).\gamma ^{\mu }.\gamma ^{\nu }\right){}_j
\bar{v} spinor contracted with a chain of Dirac matrices
DCHN[GAD[\[Mu]] . GAD[\[Nu]], SpinorVBar[p, m], j]\left(\bar{v}(p,m).\gamma ^{\mu }.\gamma ^{\nu }\right){}_j
u spinor contracted with a chain of Dirac matrices
DCHN[GAD[\[Mu]] . GAD[\[Nu]], i, SpinorU[p, m]]\left(\gamma ^{\mu }.\gamma ^{\nu }.u(p,m)\right){}_i
v spinor contracted with a chain of Dirac matrices
DCHN[GAD[\[Mu]] . GAD[\[Nu]], i, SpinorV[p, m]]\left(\gamma ^{\mu }.\gamma ^{\nu }.v(p,m)\right){}_i