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Mathematics professor at Cambridge

Feb
3
awarded  Nice Answer
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awarded  Notable Question
Nov
14
awarded  Nice Question
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20
awarded  Yearling
Oct
8
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Aug
18
awarded  Good Answer
Jul
17
awarded  Populist
Jul
8
revised Nonexistence of an approximately distance-preserving map between discrete cubes
added 779 characters in body
Jul
8
comment Nonexistence of an approximately distance-preserving map between discrete cubes
You're right about projection on to the first $n-1$ coordinates. Actually, the case that I'm really interested in is $n/2$ dimensions. In an hour or so I'll modify the question accordingly.
Jul
8
asked Nonexistence of an approximately distance-preserving map between discrete cubes
Jun
25
awarded  Excavator
Jun
25
awarded  Enlightened
Jun
22
comment Are there very strongly pseudorandom permutations?
I think I've now found a construction that does what I want.
Jun
20
comment Are there any good websites for hosting discussions of mathematical papers?
I think you can make contributions by registering directly with the site, and anybody can read it. But Google Plus is a particularly convenient way of contributing, since all you have to do is write a normal post and add the #spnetwork hashtag. In due course other social networks will be added, but Google Plus has the advantage that public posts are genuinely public.
Jun
20
comment Are there very strongly pseudorandom permutations?
Actually, scratch that -- I miscalculated the information-theoretic bound, which gives that exponentially many would be needed.
Jun
19
awarded  Nice Answer
Jun
19
awarded  Necromancer
Jun
19
comment Are there very strongly pseudorandom permutations?
I now think it may be possible to do something by composing polynomially many Feistel permutations.
Jun
19
answered Are there any good websites for hosting discussions of mathematical papers?
Jun
19
comment Are there very strongly pseudorandom permutations?
Yes. I was vague about it, but the precise requirement I would like is that $k$ should be at most a polynomial function of $n$ (or perhaps a very slightly superpolynomial function).