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Let $X$ be a topological space and $U,V \subset X$ two open subsets such that $U \cap V$ and $U \cup V$ are both simply connected. How can i show that $U$ and $V$ are simply connected? Thanks in advance.

hilary

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    yes i know. but i tried with van kampen's. but i have no idea how to apply it.2011-12-09

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