“…9, is drawn in the space of the free-energy coefficients. In order that the theoretical phase diagram reflects the experimental phase diagram, one has to follow precise rules, deduced from the theory of Singularities [12], for determining the coefficients varying with external variables (T , P , x, ...) and the form of their dependence on the external variables. 1) The number of varying coefficients should be equal to the number of external variables, i.e., one-two-or-three dimensional phase diagrams require a dependence of one-two-or-three coefficients, respectively, on the external variables.…”