#### Vol. 5, No. 3, 2011

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A categorical proof of the Parshin reciprocity laws on algebraic surfaces

### Denis Osipov and Xinwen Zhu

Vol. 5 (2011), No. 3, 289–337
##### Abstract

We define and study the $2$-category of torsors over a Picard groupoid, a central extension of a group by a Picard groupoid, and commutator maps in this central extension. Using this in the context of two-dimensional local fields and two-dimensional adèle theory we obtain the two-dimensional tame symbol and a new proof of Parshin reciprocity laws on an algebraic surface.

##### Keywords
Picard groupoids, central extensions, commutator maps, two-dimensional local fields, higher adeles, reciprocity laws
Primary: 19F15
Secondary: 18D05