 For any specific volume formula_50, denote formula_83 the function that describes how the pressure varies with the temperature formula_10, as allowed by the equation of state, when the specific volume of the material is forcefully kept constant at formula_50.Analogously, for any pressure formula_39, let formula_87 be the function that describes how the specific volume varies with the temperature, when the pressure is kept constant at formula_39.Namely, those functions are such that
for any values of formula_91.