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Mar
14
comment Approximation to colouring for bounded degree graphs
If chi(G) denotes the colouring number and not the chromatic number, you should change the notation -- maybe to col(G).
Mar
12
awarded  Yearling
Feb
12
awarded  Popular Question
Feb
10
awarded  Necromancer
Aug
5
awarded  Necromancer
Apr
21
awarded  Favorite Question
Mar
12
awarded  Yearling
Mar
5
comment Linear intersection number and coloring (not chromatic) number
What happens if you replace the colouring number with the minimum degree $+1$, or the maximum degree $+1$, or the chromatic number?
Feb
12
comment Chromatic number of graphs of tangent closed balls
A clarification: Choose the sphere $S$ to be smallest, and subject to that choose it to be extreme. I claim without proof that if a sphere kisses 12 others of equal or greater radius, then all 13 spheres have equal radius. Furthermore the sphere kissed by 12 others has its centre in the convex hull of the other 12 centres, and therefore is not extreme (of these 13 spheres) in any direction.
Oct
31
awarded  Nice Answer
Oct
16
comment Is a rigid cycle a chordal graph?
No to the second question, as exhibited by a graph on five vertices and eight edges with minimum degree 3.
Jul
2
awarded  Curious
Mar
12
awarded  Yearling
Feb
6
comment Combinatorial Proof of Weak Perfect Graph Theorem.
Thanks Petr, updated the link.
Feb
6
revised Combinatorial Proof of Weak Perfect Graph Theorem.
updated link
Jan
8
comment How dense is the set of asymmetric graphs?
Is there a simple justification for your first sentence?
Dec
6
comment Expected Value for a Connected Graph
It's easier to think about this in the equivalent model of giving each vertex a uniform random real in $[0,1]$.
Nov
9
awarded  Good Question
Oct
1
answered Does the notion of graphs with vertex multiplicity exist?
Jul
29
comment Hitting all cycles with three disjoint vertex sets
Even any graph containing $K_4$ fails.