If I'm not mistaken, G sentence is self-referential.
In PM 1st ed says that a sentence's meaning cannot be determined until its constituent's meaning is determined; if one of its constituent is the sentence itself, there is a vicious circle.
user131753
@GeorgeChen I don't think so. A G sentence for $T$ does not (and cannot) directly refer to itself - only to some (term for) a number which serves as its code according to a very concrete, peculiar choice of G numbering.
