relations between phase diagrams and free energy curves

"Equilibrium phase diagram in ideal system"
For a system in which ideal solution are formed in both liquid and solid states, the free energy curves for both states will be the form in the shown figures:
At very high temperatures such as T6 the liquid free energy curve lied below that of the solid at all compositions. With decreasing temperature the free energies of both a liquid and solid state intersect. At T5 the free energy of liquid and solid state are equal at a which represent the melting point of A where pure solid A and pure liquid A at equilibrium. At all other composition at T5 the stable condition is a single liquid solution. At T4 the liquid and solid free energy curves intersect at some intermediate composition. Under these circumstances it may be demonstrated that within a certain composition range a mixture of two solutions one liquid and one solid is more stable than either liquid solution or a solid solution. At T1 the solid solution is more stable than a liquid solution.