Dear, I would like to ask for a confirmation: if I consider a phase diagram such as the SiO₂–CaO–Al₂O₃ diagram by Osborn (1968), and I take a composition within the diagram — for example inside the tie-triangle anorthite–silica–wollastonite — can I directly apply the lever rule to determine the proportions of the three phases at the end of cooling (room temperature), without worrying about the variation of the liquid composition during the cooling process, correct? This is possible because this diagram is not an isothermal ‘slice’, right? In other words, if I am only interested in knowing the final percentages of the three phases starting from a given composition in this diagram (or also in the SiO₂–Al₂O₃–MgO system), can I immediately apply the lever rule within my tie-triangle and obtain the theoretical final percentages?