... the composition k := ψ ○ Tr k / p , whenever a nontrivial additive character of k is (implicitly or explicitly) called for (for instance in the definition of a Kloosterman sheaf, or of a hypergeometric sheaf, on ₘ/k). additive...

...-twisted Kloosterman sheaf of rank seven has G_geom = G_arith = G₂. The first task is to express its stalk at a fixed point a ɛ kˣ as the finite field Mellin transform...