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Title:
Commutators in SL_2 and Markoff Surfaces

Speaker:
Peter Sarnak

Abstract:
We discuss a local to global profinite principle for being a commutator in some arithmetic groups. Specifically we show that SL2(Z) satisfies such a principle, while it can fail with infinitely many exceptions for SL2(Z[1/p]). The source of the failure is a reciprocity obstruction to the integral Hasse Principle for cubic Markoff surfaces. Joint work with Amit Ghosh and Chen Meiri.

Link:
https://www.ias.edu/video/commutators-sl2-and-markoff-surfaces