  We consider the general framework of perturbative quantum field theory for
the pure Yang-Mills model. We give a more precise version of the Wick theorem
using Hopf algebra notations for chronological products and not for Feynman
graphs. Next we prove that Wick expansion property can be preserved for all
cases in order $ n = 2. $ However, gauge invariance is broken for chronological
products of Wick submonomials.
