(a) show that it is not posssible for a pure fluid to have a
quartenary point where the vapor, liquid,and two solid phase are
all in equilibrium.

(b) show that the specification of the overall molar volume of a
one-component, two phase mixture is not sufficient to identify the
thermodynamic state of either phase,but that the specification of
both the molar volume and molar enthalpy is sufficient to determine
the thermodynamic states of each of the phases and the distribution
of mass between the phases.