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Evaluating a p-th order cohomology operation.

J. Harper, A. Zabrodsky (1988)

Publicacions Matemàtiques

A certain p-th order cup product is detected by a p-th order cohomology operation. The result is applied to finite H-spaces, to show that several properties of compact Lie groups do not hold for arbitrary torsion free finite H-spaces.

Every braid admits a short sigma-definite expression

Jean Fromentin (2011)

Journal of the European Mathematical Society

A result by Dehornoy (1992) says that every nontrivial braid admits a σ -definite expression, defined as a braid word in which the generator σ i with maximal index i appears with exponents that are all positive, or all negative. This is the ground result for ordering braids. In this paper, we enhance this result and prove that every braid admits a σ -definite word expression that, in addition, is quasi-geodesic. This establishes a longstanding conjecture. Our proof uses the dual braid monoid and a new...

Every knot is a billiard knot

P. V. Koseleff, D. Pecker (2014)

Banach Center Publications

We show that every knot can be realized as a billiard trajectory in a convex prism. This proves a conjecture of Jones and Przytycki.

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