The paper of Eugene Babaev "Intuitive Chemical Topology Concepts" . ... These objects with quite different geometrical properties have homeomorphic 2 D surfaces, which can be continuously deformed one to another or to the same surface of a torus. ... This approach (a generalization of our earlier works [29-33]) allows us to apply the homeomorphism concept to chemical problems in a new way, classifying molecular structures and reactions from the viewpoint of the topology of surfaces. ... Surfaces . ...