Biextensions of 1-motives by 1-motives
Abstract
Let S be a scheme. In this paper, we define the notion of biextensions of 1-motives by 1-motives. If M(S) denotes the Tannakian category generated by 1-motives over S (in a geometrical sense), we define geometrically the morphisms of M(S) from the tensor product of two 1-motives M1 and M2 to another 1-motive M3, to be the isomorphism classes of biextensions of (M1,M2) by M3. Generalizing this definition we obtain, modulo isogeny, the geometrical notion of morphism of M(S) from a finite tensor product of 1-motives to another 1-motive.
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