Fppf topology

We will work in the fppf topology on the category of schemes over 5. A group scheme over S will be identified with the sheaf of abelian groups it gives rise to. A sequence G — G -+ Gft of group schemes over S will be called exact if the associated sequence of sheaves is exact. 

We use the fppf topology, but another topology would give the same result. See [BBM] Coroilaire 2,3.11. 

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