Fundamental groups and homotopy invariance
Research context
postgraduate concept · established · As of 2026-10-10
The fundamental group pi1(X,x0) consists of based loops modulo homotopies fixing endpoints, with concatenation.
Key knowledge
The fundamental group pi1(X,x0) consists of based loops modulo homotopies fixing endpoints, with concatenation. It is Z for the circle and trivial for S-n with n≥2. A homotopy equivalence induces isomorphisms of homotopy groups after suitable basepoint choices; this invariant does not alone classify spaces. Maps and basepoints, rather than pictures of apparent holes, determine the group.
Conditions and scope
- Based loops and endpoint-fixed homotopies are used; concatenation orientation is specified.
- Change of basepoint in a path-connected space yields an isomorphism that is generally not canonical.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: §1.1 paths/fundamental group and §2.1 chains, cellular homology pp. 137–141 including surface computations. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
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