Phase diagrams of classical lattice systems continuation

III. Contour Models
In this section we introduce contour models and study some of their properties. In $\text{Sec}$. V we shall show that every pure thermodynamic phase which we construct can be described by means of a suitably chosen contour model. In the language of contour models one can clearly elucidate what is meant by the expression “typical configurations of every phase are small perturbations of a corresponding ground state”.