Name: Sun Qingfeng (email_not_shown)
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:

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

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