Читать книгу Invariants And Pictures: Low-dimensional Topology And Combinatorial Group Theory - Vassily Olegovich Manturov - Страница 10

In this section we discuss diagrammatic language of group description. This approach was first discovered and used by van Kampen [van Kampen, 1933]. The essence of his discovery was an interconnection between combinatorially-topological and combinatorially-group-theoretical notions. The gist of this approach is a presentation of groups by flat diagrams (that is, geometrical objects, — flat complexes, — on a plane or other surfaces, such as a sphere or a torus). We review this theory following [Olshanskii, 1989].