Geodesic
Ultrafunctor
Canadian journal of mathematics, Tome 27 (1975) no. 2, pp. 372-375

Voir la notice de l'article provenant de la source Cambridge University Press

Let G be a functor from commutative rings to abelian groups and let {Rt : i ∈ S} be a family of commutative rings indexed by the set S. Let be an ultrafilter on S, and let denote the ultraproduct of the Rt with respect to . This paper studies the problem of computing from the G(Rj) via the map The functors studied are Pic = Picard group, Br = Brauer group, U = units, and the functors K0, K1, SK1, K2 of Algebraic K-Theory. For G = Pic, U, K1 and SK1, (*) is always a monomorphism. An example is given to show that even if all the Rt are finite fields the map (*) has a kernel for G = K2. 
Magid, Andy R. Ultrafunctor. Canadian journal of mathematics, Tome 27 (1975) no. 2, pp. 372-375. doi: 10.4153/CJM-1975-045-9
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