“…Such topological invariants include: the Euler characteristic, surface genus, connectivity, type and Poincaré index of a singular point. Topological properties of phase diagrams are considered in the literature [ 2 , 3 , 4 , 5 , 6 , 7 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]: vapor–liquid equilibrium [ 2 , 3 , 4 , 5 , 6 , 7 , 11 , 12 ], liquid–liquid equilibrium [ 13 , 14 , 15 ] and liquid–solid equilibrium (LSE) [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ].…”