3,981 reputation
2145
bio website quora.com/Alon-Amit
location Los Altos, CA
age 45
visits member for 5 years, 1 month
seen 2 days ago

Dabbler in things.


Mar
19
revised What are the worst notations, in your opinion ?
added 24 characters in body
Mar
19
comment What are the worst notations, in your opinion ?
@Qiaochu: I'm really only talking about the interior case. It's then that the \osum is the same subspace as the sum but with the implied additional condition on the subspaces.
Mar
19
comment how slow can the dimension of a product set grow?
So the circle S^1 has dimension 2 in your sense? If so, I don't know if this has a name but I certainly wouldn't recommend "dimension".
Mar
19
comment What are the worst notations, in your opinion ?
@Francois: Sheesh, of course. Sorry. Fixed.
Mar
19
revised What are the worst notations, in your opinion ?
deleted 4 characters in body; added 11 characters in body
Mar
18
answered What are the worst notations, in your opinion ?
Mar
17
comment Fundamental groups of noncompact surfaces
If I had been faster I would have proposed the same reference so you wouldn't have had to advertise your own book. I'm a fan :-)
Mar
16
comment Properties of Graphs with an eigenvalue of -1 (adjacency matrix)?
If G->B is a covering map (in the topological sense), then G inherits all the eigenvalues of B (just choose an eigenfunction that is uniform on the fibers). So, for instance, any graph which covers K_n for any n has -1 as an eigenvalue. The cycle of length 3k covers the triangle, which is another way to explain Kevin's example.
Mar
16
awarded  Nice Answer
Mar
16
awarded  Popular Question
Mar
14
awarded  Enlightened
Mar
14
awarded  Nice Answer
Mar
12
comment Books you would like to see translated into English.
That's +10 from me, too.
Mar
10
answered A historical question: Hurwitz, Luroth, Clebsch, and the connectedness of M_g
Mar
9
revised Why are the sporadic simple groups HUGE?
added 2 characters in body
Mar
9
comment If $2^x $and $3^x$ are integers, must $x$ be as well?
This answer was given by Gerry. I just added the link to Wikipedia.
Mar
9
revised If $2^x $and $3^x$ are integers, must $x$ be as well?
Added wikipedia link
Mar
9
comment If $2^x $and $3^x$ are integers, must $x$ be as well?
Very interesting! Just to make sure I understand - does this generalize the "n^x for all n" version only, or can it be applied to "2,3,5" and "2,3" as well?
Mar
9
accepted If $2^x $and $3^x$ are integers, must $x$ be as well?
Mar
9
comment If $2^x $and $3^x$ are integers, must $x$ be as well?
@jef: the best hint I can think of is "calculus of differences".