Is the disjoint union of an arbitrary number of $n$-manifolds, again a $n$-manifold?
I only found a result that proves this for countably many manifolds.
Is the disjoint union of an arbitrary number of $n$-manifolds, again a $n$-manifold?
I only found a result that proves this for countably many manifolds.
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That depends upon your definition of manifold, but by the usual definition they are second countable. And that excludes the possibility of being an infinite non-countable union of disjoint manifolds.