[OS X TeX] \label{n!} yields "n\protect !" in the margin

[Hendrik Chaltin]

Dear colisters,

If I choose as label
\label{n!}
, I get, on the preview,
n\protect !
in the margin.
According to Kopka & Daly 3rh ed. p. 224 ! is not one of the 
"forbidden" symbols
and according to the 4th ed. p. 211 there are actually none (?!?).

I can, of course, use another label, such as \label{nfact},
but I am a curious person:
did I perhaps call a package in my preamble
that is responsible for this?

Thanks,

HC

I use TeXShop, if that matters.

  

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