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Consider the letter T (written as such: thus we have two line segments).
1) Prove that it is impossible to to place uncountably many copies of the letter T disjointly in the plane ##\mathbb{R}^2##.
2) Prove that it is impossible to place uncountably many homeomorphic copies of the letter T disjointly in the plane.
3) For which letters in the alphabet is (2) possible? The letters are written as follows
A B C D E F G H J I J K L M N O P Q R S T U V W X Y Z
4) Let ##U\subseteq \mathbb{R}^3## be shaped like an umbrella: it is a disc (with boundary) with a perpendicular segment attached to its center. Prove that uncountably many copies of ##U## cannot be placed disjointly in the space ##\mathbb{R}^3##.
5) What happens to 4 if the line segment is attached to the boundary of the disc instead?
(Source: Pugh's Real mathematical analysis)
Please list any sources that you have used to solve this question. Using google or other search engines is forbidden. Wikipedia is allowed but not its search engine. Wolfram alpha and other mathematical software is allowed.
Points will be given as follows:
1) First person to post a correct solution to one of the above points will receive 3 points (So if you solved 3 and 4, you will receive 6 points).
2) Anybody to post a (original) correct solution to one of the above points will receive 1 point.
3) Anybody posting a (nontrivial) generalization of some of the above questions will receive 2 points
4) The person who posts a solution with the least advanced mathematical machinery will receive 1 extra point for his solution (for example, somebody solving this with basic calculus will have an "easier" solution than somebody using singular homology), if two people use the same mathematical machinery, then we will look at how complicated the proof is.
5) The person with the most elegant solution will receive 1 extra point for his solution (I decide whose solution is most elegant)
Please thank this post if you think this is an interesting challenge (no, I'm not doing this to get more thanks, I just want to see if I should post more things like this and the "thanks" system is the easiest way for this).
Private messages with questions, problem suggestions, etc. are always welcome!
1) Prove that it is impossible to to place uncountably many copies of the letter T disjointly in the plane ##\mathbb{R}^2##.
2) Prove that it is impossible to place uncountably many homeomorphic copies of the letter T disjointly in the plane.
3) For which letters in the alphabet is (2) possible? The letters are written as follows
A B C D E F G H J I J K L M N O P Q R S T U V W X Y Z
4) Let ##U\subseteq \mathbb{R}^3## be shaped like an umbrella: it is a disc (with boundary) with a perpendicular segment attached to its center. Prove that uncountably many copies of ##U## cannot be placed disjointly in the space ##\mathbb{R}^3##.
5) What happens to 4 if the line segment is attached to the boundary of the disc instead?
(Source: Pugh's Real mathematical analysis)
Please list any sources that you have used to solve this question. Using google or other search engines is forbidden. Wikipedia is allowed but not its search engine. Wolfram alpha and other mathematical software is allowed.
Points will be given as follows:
1) First person to post a correct solution to one of the above points will receive 3 points (So if you solved 3 and 4, you will receive 6 points).
2) Anybody to post a (original) correct solution to one of the above points will receive 1 point.
3) Anybody posting a (nontrivial) generalization of some of the above questions will receive 2 points
4) The person who posts a solution with the least advanced mathematical machinery will receive 1 extra point for his solution (for example, somebody solving this with basic calculus will have an "easier" solution than somebody using singular homology), if two people use the same mathematical machinery, then we will look at how complicated the proof is.
5) The person with the most elegant solution will receive 1 extra point for his solution (I decide whose solution is most elegant)
Please thank this post if you think this is an interesting challenge (no, I'm not doing this to get more thanks, I just want to see if I should post more things like this and the "thanks" system is the easiest way for this).
Private messages with questions, problem suggestions, etc. are always welcome!