a. Show that it is not possible for a pure fluid to have a quartenary point where the vapor, liquid, and two solid phases 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 the molar enthalpy (or any two other molar properties) is sufficient to determine the thermodynamic states of each of the phases and the distribution of mass between the phases.