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math.CT2026
Groupoid G-spans and matrices over group rings
Joachim Kock, Jesper M. Møller
When G is a finite abelian group, we define G-spans of groupoids and their associated matrices with entries in the group ring QG and show that composition of spans corresponds to m…
math.CT2026
Signs in objective linear algebra, exemplified with exterior powers and determinants
Joachim Kock, Jesper Michael Møller
We develop objective linear algebra in a new setting with a cardinality functor that can take negative values. The signs arise as little homotopies, as ratios between orientations.…