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14
votes
What is the fewest number of points you must delete from $\mathbb{R}^3$ to make it not simpl...
The simply connected deletion number equals the continuum. This follows from the fact that for any dense subset $A$ in the real line the subset $A_3=(A\times \mathbb R\times \mathbb R)\cup (\mathbb R\ …
5
votes
Accepted
Must an inverse limit of simply connected groups be simply connected?
It seems that the inverse limit of simply connected Lie groups is simply connected. The argument uses the well-known fact that the second homotopy group of any Lie group is trivial (see e.g. Homotopy …