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seen Sep 23 at 12:12

Jul
2
awarded  Curious
Apr
26
accepted Lower bound of crossing number (minimum) of K7
Apr
22
comment Lower bound of crossing number (minimum) of K7
I thought R. Guy (1972) proved (n^4)/80+O(n^3) <= nu(Kn) <= (n^4)/64+O(n^3), but the big-O notation doesn't help me here. I'll read your link carefully. Thanks.
Apr
21
revised Lower bound of crossing number (minimum) of K7
deleted 481 characters in body
Apr
21
revised Lower bound of crossing number (minimum) of K7
deleted 179 characters in body
Apr
21
asked Lower bound of crossing number (minimum) of K7
Apr
10
accepted Is there a not hand-waving way to prove any wheel graph is self-dual?
Apr
10
comment Is there a not hand-waving way to prove any wheel graph is self-dual?
Ah, the balloon poking thing. I really like this answer and the humor. A bit overkill, though.
Apr
10
asked Is there a not hand-waving way to prove any wheel graph is self-dual?
Mar
15
accepted Prove Γ ⊢ ¬¬φ is formally provable from Γ ⊢ φ
Mar
15
asked Prove Γ ⊢ ¬¬φ is formally provable from Γ ⊢ φ
Jan
25
accepted Validity of proving “No surjection from any set to the its powerset” using induction on the cardinality of powerset
Jan
25
comment Validity of proving “No surjection from any set to the its powerset” using induction on the cardinality of powerset
Could you help me with the "prove by contradiction" in the link? The 3rd line from the end of the proof, what is "A=f(a)"? I thought A is the domain and f(a) is an element of the range.
Jan
25
asked Validity of proving “No surjection from any set to the its powerset” using induction on the cardinality of powerset
Jan
25
comment Hilbert Hotel: what if countably many buses each with countably many guests arrived?
btw, did you mean "associate the n-th guest from the k-th bus to the number found by raising the n-th prime number to the (k+1)-th power"? The wording upstairs is a little bit confusing.
Jan
25
comment Hilbert Hotel: what if countably many buses each with countably many guests arrived?
btw, I knew that the power set of a countable set is uncountable, so I think there is a boundary somewhere
Jan
25
comment Hilbert Hotel: what if countably many buses each with countably many guests arrived?
This is exactly what I had in mind, but I was not sure about the part for moving the guests. Thank you!
Jan
25
comment Hilbert Hotel: what if countably many buses each with countably many guests arrived?
So there is no "bound for the order" for countability? Is it possible to create a mapping f: N->N^3? Something like countable ships holding countable buses with countable tourists arrived at the harbor near Hilbert's Hotel...
Jan
25
awarded  Editor
Jan
25
revised Hilbert Hotel: what if countably many buses each with countably many guests arrived?
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