Solution
ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2017/ii/paper-1/20i/e/solution
Past exam of the mathematics course of the University of Cambridge 2017 ii Paper 1 20I e Solution by
Codex 0 Created 2026-09-24 Updated 2026-10-05
Let be the two oriented circle generators of the fundamental group of a bouquet of circles, . TakeTheir loops are freely homotopic: slide the basepoint of the loop along the path , thereby introducing the route to the original loop and back. Equivalently the change-of-basepoint construction along a loop realizes conjugation, and the retraced connecting portions can be contracted with a moving marked point.
They are not based homotopic, since their reduced words in the free group are distinct: has length one and has length three with no cancellation. This illustrates that free homotopy remembers conjugacy classes, whereas based homotopy remembers actual elements of the fundamental group.
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