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FLT.AutomorphicForm.QuaternionAlgebra.HeckeOperators.Concrete

theorem QuotientGroup.mk_image_finite_of_compact_of_open {G : Type u_1} [Group G] [TopologicalSpace G] [IsTopologicalGroup G] {g : G} {U V : Subgroup G} (hU : IsCompact U) (hVopen : IsOpen V) :
(mk '' (U * {g})).Finite

The Hecke operator T_v as an R-linear map from R-valued quaternionic weight 2 automorphic forms of level U_1(S).

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      The (global) matrix element (unipotent t) * (diag α hα) = !![α, t; 0, 1]. Here t ∈ 𝒪ᵥ / α and we lift it arbitrarily to 𝒪ᵥ.

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          The set of elements unipotent_mul_diag, that is, the elements of (D ⊗ 𝔸_F^∞)ˣ which are (α t;0 1) at v and the identity elsewhere, as t runs through a set of coset reps of 𝓞ᵥ / α. These will form a set of coset representatives for U1 diag U1.

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              The Hecke operator U_{v,α} associated to the matrix (α 0;0 1) at v, considered as an R-linear map from R-valued quaternionic weight 2 automorphic forms of level U_1(S). Here α is a nonzero element of 𝓞ᵥ. We do not demand the condition v ∈ S, the bad primes, but this operator should only be used in this setting. See also T r v for the good primes.

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                  theorem Ne.mul {M₀ : Type u_4} [Mul M₀] [Zero M₀] [NoZeroDivisors M₀] {a b : M₀} (ha : a 0) (hb : b 0) :
                  a * b 0

                  HeckeAlgebra F D r S R is the Hecke algebra associated to the weight 2 R-valued automorphic forms associated to the discriminant 1 totally definite quaternion algebra D over the totally real field F, of level U₁(S) where S is a finite set of nonzero primes v of 𝓞 F. To make sense of this definition we choose a rigidification r, that is, a fixed 𝔸_F^∞-linear isomorphism D ⊗[F] 𝔸_F^∞ = M₂(𝔸_F^∞), enabling us to define level structures and Hecke operators Tᵥ and Uᵥ using 2x2 matrices.

                  Details: U₁(S) is the subgroup of (D ⊗[F] 𝔸_F^∞)ˣ associated, via r, to the matrices which are in GL₂(𝓞ᵥ) for all v ∉ S and which are of the form (a *; 0 a) mod v for all v ∈ S. The Hecke algebra is defined to be the sub-R-algebra of the weight 2 forms of level U₁(S) generated by the following two kinds of Hecke operators: first there are the operators Tᵥ associated to the matrices (ϖᵥ 0; 0 1) for v ∉ S (here ϖᵥ ∈ 𝔸_F^∞ is a local uniformiser supported at v). Second, there are the Hecke operators Uᵥ,ₐ for v ∈ S and 0 ≠ αᵥ ∈ 𝓞ᵥ, associated the matries (αᵥ 0; 0 1). These slightly nonstandard Hecke operators satisfy Uᵥ,ₛ * Uᵥ,ₜ = Uᵥ,ₛₜ and in particular this Hecke algebra is commutative (Hecke operators supported at distinct primes commute because the decomposition of the double cosets into single cosets can be done purely locally).

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