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Monthly Archives: July 2009
BrianchonGramSommerville and ideal hyperbolic Dehn invariants
A beautiful identity in Euclidean geometry is the BrianchonGram relation (also called the GramSommerville formula, or Gram’s equation), which says the following: let be a convex polytope, and for each face of , let denote the solid angle along the … Continue reading
scl, sails and surgery
I have just uploaded a paper to the arXiv, entitled “Scl, sails and surgery”. The paper discusses a connection between stable commutator length in free groups and the geometry of sails. This is an interesting example of what sometimes happens … Continue reading
van Kampen soup and thermodynamics of DNA
The development and scope of modern biology is often held out as a fantastic opportunity for mathematicians. The accumulation of vast amounts of biological data, and the development of new tools for the manipulation of biological organisms at microscopic levels … Continue reading
Posted in Biology, Dynamics, Groups
Tagged biological computation, DNA, fatgraphs, free groups, Holliday junction, scl, thermodynamics, van Kampen diagrams
4 Comments
Orderability, and groups of homeomorphisms of the disk
I have struggled for a long time (and I continue to struggle) with the following question: Question: Is the group of selfhomeomorphisms of the unit disk (in the plane) that fix the boundary pointwise a leftorderable group? Recall that a … Continue reading
Posted in Dynamics, Groups
Tagged BurnsHale, distortion, Dynamics, orderable groups, quasimorphisms, Thurston stability theorem
4 Comments
Amenability of Thompson’s group F?
Geometric group theory is not a coherent and unified field of enquiry so much as a collection of overlapping methods, examples, and contexts. The most important examples of groups are those that arise in nature: free groups and fundamental groups … Continue reading →