HOMEWORK 4 – 2022
Exercise 1. Prove that the plane X is not homeomorhic with the union Y of two
planes which have a line as an intersection. Hint: Compute homology groups of pairs
(X, X − {p}) and (Y, Y − {q}), where p ∈ X is a point and q ∈ Y is a point in the
intersection of planes. Use excision theorem.
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