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1d

comment 
Can all unitdistance graphs have their vertices at algebraic integers?
Thanks! The link to the first one was in my answer, but I did not know about the second. 
2d

awarded  Nice Answer 
2d

comment 
Can all unitdistance graphs have their vertices at algebraic integers?
@David: Do you know the exact reference? 
Jan 26 
revised 
Can all unitdistance graphs have their vertices at algebraic integers?
Remark has been expanded 
Jan 26 
answered  Can all unitdistance graphs have their vertices at algebraic integers? 
Jan 26 
comment 
Can all unitdistance graphs have their vertices at algebraic integers?
@Dima: Not much difference. A hexagonal lattice maps to $K_3$... 
Jan 26 
comment 
Irreducibility of a polynomial
Sorry, I do not understand why this question is closed. 
Jan 26 
comment 
Can all unitdistance graphs have their vertices at algebraic integers?
@Dima: I just meant that two such roots with a zero form a triangle. So you may consider homomorphisms to a 6wheel (which pass to $K_3$ though). 
Jan 26 
comment 
Can all unitdistance graphs have their vertices at algebraic integers?
@Dima: The 6th degree roots of unity are algebraic integers. 
Jan 23 
comment 
Is mean width a Dehn invariant?
I do not think $W$ is invariant under scissor congruence. Compare the orders of magnitude of mean widths of $1\times 1\times N^3$ amd $N\times N\times N$ boxes. 
Jan 21 
answered  Density of tuples of conjugate algebraic numbers 
Jan 13 
comment 
What is the smallest 4chromatic graph of girth 5?
Since $\delta\geq 3$, we may estimate $\Delta$ better. Take any vertex of degree $\Delta$; all its $\Delta$ neighbors, as well as their $\geq (\delta1)\Delta$ other neighbors are distinct (due to the girth condition), so there are at least $1+\Delta\delta$ vertices at all. Thus, if $\Delta\geq 7$ then there are at least 22 vertices, and we may assume $\Delta\leq 6$. 
Dec 16 
answered  A proposition on cyclic group 
Dec 3 
comment 
Fixed point of fatness
@PietroMajer: They are. The critical situation is a rhombus with angles $\pi/3$ and $2\pi/3$; then it is 2fat, and it can be cut into two isosceles triangles, which are also 2fat. 
Nov 30 
comment 
Existence of solution for this set of polynomial equations
In your second system, shouldn't there be $(1t_i)^k$ instead of $(t_i)^k$? 
Nov 27 
answered  ncube connectivity problem 
Nov 26 
revised 
A question about generalized Dyck words
added 14 characters in body 
Nov 26 
revised 
A question about generalized Dyck words
added 9 characters in body 
Nov 26 
answered  A question about generalized Dyck words 
Nov 24 
revised 
Distribution of the permanent modulo $p$
added 6 characters in body 