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→top: clarified tagged section about def in manifold theory, typed up the definitions in TeX |
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*the [[Closure (topology)|closure]] of ''<math>S</math>'' minus the [[Interior (topology)|interior]] of <math>S</math>: <math>\partial S := \bar{S} \setminus S^\circ</math>
*the intersection of the closure of ''<math>S</math>'' with the closure of its [[complement (set theory)|complement]]: <math>\partial S := \overline{S} \cap \overline{(X \setminus S)} </math>
*the set of points <math>p \in X</math> such that every [[neighborhood (topology)|neighborhood]] of <math>p</math> contains at least one point of ''<math>S</math>'' and at least one point not of ''<math>S</math>'': <math>\partial S := \{ p \in X
== Examples ==
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