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// Split from the original oversized module; keep included in order.
include!;
include!;
include!;
include!;
include!;
/// Closed-form scalar building blocks for Riesz, Matérn, and isotropic
/// hybrid Duchon kernels.
///
/// Fourier convention: f̂(ω) = ∫ e^{-iω·x} f(x) dx,
/// f(x) = (2π)^{-d} ∫ e^{iω·x} f̂(ω) dω.
///
/// Riesz kernel: R_j^d(r) = F^{-1}{|ρ|^{-2j}}(r).
/// Matérn block: M_ℓ^d(r; κ) = F^{-1}{(|ρ|² + κ²)^{-ℓ}}(r).
include!;