#### Vol. 313, No. 1, 2021

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Convolution algebras for relational groupoids and reduction

### Ivan Contreras, Nima Moshayedi and Konstantin Wernli

Vol. 313 (2021), No. 1, 75–102
DOI: 10.2140/pjm.2021.313.75
##### Abstract

We introduce the notions of relational groupoids and relational convolution algebras. We provide various examples arising from the group algebra of a group $G$ and a given normal subgroup $H$. We also give conditions for the existence of a Haar system of measures on a relational groupoid compatible with the convolution, and we prove a reduction theorem that recovers the usual convolution of a Lie groupoid.

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