Name: Sun Qingfeng Date: 07/02/15-12:50:11 PM Z


I see, Thanks for the detailed reply.

BTW, when I test the FC9.0, I am confused by the output:
Input:
DiracTrace[GA[\[Mu]].GA[\[Nu]]]

Output:
Factoring[4 Pair[LorentzIndex[\[Mu]], LorentzIndex[\[Nu]]]]

In the previous version(8.20) the output seems to be:
4 Pair[LorentzIndex[\[Mu]], LorentzIndex[\[Nu]]]
My Mathematica version is 10.1