Does there exist a set in usual Euclidean space such that for every plane the intersection is finite and nonempty ?
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I'm not sure I'm posting this in a right Forum.
Does there exist a set in usual Euclidean space such that for every plane the intersection is finite and nonempty ?
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I'm not sure I'm posting this in a right Forum.
To determine if there exists a set in usual Euclidean space such that for every plane , the intersection is finite and nonempty, we need to consider a construction that satisfies these conditions.
One possible approach is to construct the set using a version of the "space-filling curve" concept, but within certain constraints. However, space-filling curves like the Peano or Hilbert curves fill an entire region and would not make the intersection with a plane finite, thus a different approach is needed.
Instead, consider the following construction:
Construct the set by taking a dense set of points on every line parallel to one of the coordinate axes, such that these points are sparse in other coordinate directions. One way to do this is:
- For a subset of lines along the -axis, -axis, and -axis (in ), include points spaced in such a way that each point belongs to a single line only. Specifically, for each integer point on the -axis of the form , place a point .
This construction ensures:
1. Non-empty intersection: For any plane in , there will be at least one axis-aligned line passing through or intersecting this plane at some point, and since we have points densely populating these lines, is nonempty.
2. Finite intersection: Given the specific choice of constructing sparse points only on one type of line, the intersection of any plane with these lines would result in a finite number of points on that plane.
Thus, the set satisfies the conditions of having finite and nonempty intersections with any plane .
Therefore, it is indeed possible to construct such a set .
The existence of such a set in usual Euclidean space is conclusively: