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## 2009/09/05

### Urysohn lemma

There is an idea more general than the idea of simple connectedness, an idea that includes simple connectedness as a special case. It involves a certain group that is called the fundamental group of the space. Two spaces that are homeomorphic have fundamental groups that are isomorphic. And the condition of simple connectedness is just the condition that the fundamental group of X is the trivial (one-element) group.

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XOO9/05/2009 5:44 pm 說：

homotopy 其實是個很不好算的東西 ...~_~

Hsien-Chih Chang9/20/2009 5:53 am 說：

BTW, 我覺得有 emotion 才會有 intuition，雖然可能跟你的想法不合XD

Josh Ko9/20/2009 9:12 am 說：