NonCommQ[exp] yields True if
exp contains non-commutative objects (i.e. those objects
which are listed in $NonComm) not inside
DiracTraces or SUNTraces.
Overview, $NonComm, NonCommFreeQ, DiracTrace, SUNTrace.
NonCommQ[xx + yy]\text{False}
NonCommQ[GA[\[Mu]] . GS[p + m] . GA[\[Mu]]]\text{True}
NonCommQ[DCHN[GA[\[Mu]], i, j]]\text{True}