Bourbaki

Exercise 9, § 5

Tag 0412, permanent. Cite it as [Bourbaki, Tag 0412].

Algebraic Topology, IV, p. 465

Let X be a topological space, let R be an equivalence relation in X and let p:X→X/Rp: X\rightarrow X/R be the canonical surjection. Let x∈Xx\in X.

(a) Suppose that X is connected and locally arcwise connected, that the equivalence classes are connected sets, and that the space X/RX/R is unravelable. Prove that the homomorphism p∗:π1(X,x)→π1(X/R,p(x))p_*:\pi_1(X, x)\rightarrow \pi_1(X/R, p(x)) is surjective.

(b) Suppose that X=IX =\mathbf{I} and that {0,1}\{0,1\} is the only equivalence class which is not reduced to an element. Prove that the homomorphism p∗p_* is not surjective.

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Machine translation of the English, by gpt-5-6-mini. Not checked by a person. That model is a cut down version of the one the rest of this language was written by.