Paper 1, Section II, G

Metric and Topological Spaces | Part IB, 2013

Consider the sphere S2={(x,y,z)R3x2+y2+z2=1}S^{2}=\left\{(x, y, z) \in \mathbb{R}^{3} \mid x^{2}+y^{2}+z^{2}=1\right\}, a subset of R3\mathbb{R}^{3}, as a subspace of R3\mathbb{R}^{3} with the Euclidean metric.

(i) Show that S2S^{2} is compact and Hausdorff as a topological space.

(ii) Let X=S2/X=S^{2} / \sim be the quotient set with respect to the equivalence relation identifying the antipodes, i.e.

(x,y,z)(x,y,z)(x,y,z)=(x,y,z) or (x,y,z)(x, y, z) \sim\left(x^{\prime}, y^{\prime}, z^{\prime}\right) \Longleftrightarrow\left(x^{\prime}, y^{\prime}, z^{\prime}\right)=(x, y, z) \text { or }(-x,-y,-z)

Show that XX is compact and Hausdorff with respect to the quotient topology.

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