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arXiv · 2205.07691

A pleasant exercise

Jean-Pierre Labesse
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Abstract

In the Proceedings of the AMS Boulder conference in 1965 Langlands states a combinatorial lemma involving families of characteristic functions attached to ordered partitions of an obtuse basis in a finite dimensional euclidean vector space. Langlands does not give any indication about the proof of the lemma which is said to be a "pleasant exercise". Since we did not find a proof in the literature we decided to give one. We believe it of some interest for the history of the subject.

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Jean-Pierre Labesse. 2022-05-16. A pleasant exercise. https://arxiv.org/abs/2205.07691

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