  Well known from the sixties, the pressure of e.g. massless phi-four theory
may be written as a series of 2PI-diagrams (skeletons) with the lines fully
dressed. Varying the self-energy Pi in this expression, it turns into a
functional U[Y] having a maximum in function space at Y=Pi. There is also the
Feynman-Jensen thermal variational principle V[S], a potentially
non-perturbative tool. Here actions S are varied.
  It is shown, through a few formal but exact steps, that the functional U is
covered by V. The corresponding special subset of trial actions is made
explicit.
