I'm confused about the concept of a "boundary" in topology – specifically, in studying manifolds. What is the difference between a boundary existing (or rather, not existing) and a boundary being empty? To put it more clearly, if a boundary of a manifold is empty, then does that still imply that a boundary exists?
2026-03-25 23:08:27.1774480107
What is the difference between a boundary *existing* (or rather, *not* existing) and a boundary *being empty*?
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