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kathrynag
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Homework Statement
If D[tex]\subset[/tex]R, then x[tex]\in[/tex]D is said to be the interior point of D iff there is a neighborhood Q of x such that Q[tex]\subset[/tex]D. Define [tex]D^{\circ}[/tex] to be the set of interior points of D. Prove that [tex]D^{\circ}[/tex] is open and that if S is any open set contained in D, then S[tex]\subset[/tex][tex]D^{\circ}[/tex]. [tex]D^{\circ}[/tex] is called the interior of D.
Homework Equations
The Attempt at a Solution
So, we have a neighborhood [x-[tex]\epsilon,x+\epsilon[/tex]].