- #1
julypraise
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Homework Statement
Let [itex]X[/itex] be a metric space, and [itex]A[/itex] its nonempty proper subset. Then is [itex]\partial A[/itex] not open? If it is, how do I prove it?
Could you give me just some hints, not the whole solution?
Homework Equations
The Attempt at a Solution
I cannot even start..
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