  The positivity of the integrand of certain Euclidean space functional
integrals implies that the free energy per unit volume for QCD with a baryon
chemical potential $\mu_B$ (and zero isospin chemical potential) is greater
than the free energy with isospin chemical potential $\mu_I = (2 \mu_B)/N_c$
(and zero baryon chemical potential). This relation implies a bound on the
nucleon mass: there exists a particle X in QCD such that $M_N \ge (N_c m_X)/(2
I_X)$ where $m_X$ is the mass and of the particle and $I_X$ is its isospin.
