Category Archives: Exercises

Invariance of domain and its friends

We recall the theorem on invariance of domain and derive some of its variants. We’ll follow J. Vick’s Homology Theory: An Introduction to Algebraic Topology (2nd edition). The invariance of domain is stated as follows: Theorem. Suppose that are homeomorphic … Continue reading

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A simple exercise about abelian groups

Let be a group. Suppose there is an integer such that for . Prove that is abelian. Solution. Let . By we have . On the other hand we have where we have used again to obtain the last equality. … Continue reading

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