Van Kampen Diagrams

Some articles on van, diagrams, van kampen diagram:

Van Kampen Diagram - Generalizations and Other Applications
... There are several generalizations of van-Kampen diagrams where instead of being planar, connected and simply connected (which means being homotopically equivalent to a disk) the ... A particularly important one of these is the notion of an annular van Kampen diagram, which is homotopically equivalent to an annulus ... Annular diagrams, also known as conjugacy diagrams, can be used to represent conjugacy in groups given by group presentations ...

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