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Ancient/folklore
Fundamental group torsion for subsets of Euclidean 3-space ★★
Author(s): Ancient/folklore
Problem Does there exist a subset of
such that its fundamental group has an element of finite order?
![$ \mathbb R^3 $](/files/tex/6b91b713c8efe5b40b75f24aada116a325018073.png)
Keywords: subsets of euclidean space; torsion
Which homology 3-spheres bound homology 4-balls? ★★★★
Author(s): Ancient/folklore
Problem Is there a complete and computable set of invariants that can determine which (rational) homology
-spheres bound (rational) homology
-balls?
![$ 3 $](/files/tex/4aaf85facb6534fd470edd32dbdb4e28f6218190.png)
![$ 4 $](/files/tex/1f1498726bb4b7754ca36de46c0ccdd09136d115.png)
Keywords: cobordism; homology ball; homology sphere
Odd perfect numbers ★★★
Author(s): Ancient/folklore
Conjecture There is no odd perfect number.
Keywords: perfect number
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