A pleasant exercise
Group Theory
2023-11-06 v4
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.
Cite
@article{arxiv.2205.07691,
title = {A pleasant exercise},
author = {Jean-Pierre Labesse},
journal= {arXiv preprint arXiv:2205.07691},
year = {2023}
}