  In the context of many-fermion systems, "correlation" refers to the
inadequacy of an independent-particle model. Using "free" states as archetypes
of our independent-particle model, we have proposed a measure of correlation
that we called "nonfreeness" [Int. J. Quant. Inf. 5, 815 (2007)]. The
nonfreeness of a many-fermion state was defined to be its entropy relative to
the unique free state with the same 1-matrix.
  In this article, we prove that the nonfreeness of a state is the minimum of
its entropy relative to all free states. We also extend the definition of
nonfreeness to many-boson states and discuss a couple of examples.
