We say that a closed subset C of a metric space X
is nowhere-dense if and only if C contains no non
-empty open subset of X. Prove the Baire Category
Theorem: When X is a complete metric space, there
does not exist a countable collection
{C_γ包含於X:γ屬於Ν} of nowhere-dense closed subsets
of X satisfying X = ∪C_γ, γ屬於Ν.
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