The Seifert–Van Kampen Theorem
In this chapter we develop the techniques needed to compute the fundamental groups of finite CW complexes, compact surfaces, and a good many other spaces as well. The basic tool is the Seifert–Van Kampen theorem, which gives a formula for the fundamental group of a space that can be decomposed as the union of two open, path-connected subsets whose intersection is also path-connected.
KeywordsSpan Tree Fundamental Group Euler Characteristic Free Product Compact Surface
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