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Project-declaredLean 4.32.0 · mathlib@81a5d257c8e4

Classical carleson

classical_carleson

Plain-language statement

For every continuous, 2π2\pi-periodic function f:RCf : \mathbb{R} \to \mathbb{C}, the symmetric partial Fourier sums SNf(x)S_N f(x) converge to f(x)f(x) for almost every xRx \in \mathbb{R}.

Exact Lean statement

theorem classical_carleson {f : ℝ → ℂ} (cont_f : Continuous f) (periodic_f : f.Periodic (2 * π)) :
    ∀ᵐ x, Tendsto (S_ · f x) atTop (𝓝 (f x))

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
theorem classical_carleson {f :   ℂ} (cont_f : Continuous f) (periodic_f : f.Periodic (2 * π)) :    ᵐ x, Tendsto (S_ · f x) atTop (𝓝 (f x)) := by  -- Reduce to a.e. convergence on [0,2π]  apply @Function.Periodic.ae_of_ae_restrict _ two_pi_pos 0  · rw [Function.Periodic]    intro x    conv => pattern S_ _ _ _; rw [partialFourierSum_periodic]    conv => pattern f _; rw [periodic_f]  apply ae_restrict_of_ae_eq_of_ae_restrict Ico_ae_eq_Icc.symm  rw [zero_add]  -- Show a.e. convergence on [0,2π]  rw [Measure.restrict_congr_set Ioc_ae_eq_Icc.symm]  exact carleson_interval' cont_f periodic_f
Project
Carleson formalization
License
Apache-2.0
Commit
74ef907d6bdb
Source
Carleson/Classical/ClassicalCarleson.lean:131-143

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Related declarations

Project-declaredLean 4.32.0

Ae tendsto zero of distribution le

ae_tendsto_zero_of_distribution_le

Plain-language statement

Suppose that, for every error threshold δ>0\delta>0 and every measure tolerance ε>0\varepsilon>0, one can choose N0N_0 so that the set where supN>N0f(x)FN(x)\sup_{N>N_0}\lVert f(x)-F_N(x)\rVert exceeds δ\delta has measure at most ε\varepsilon. Then FN(x)F_N(x) converges to f(x)f(x) for almost every xx.

harmonic analysisFourier analysismeasure theory

Source project: Carleson formalization

Person-level attribution pending.

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Project-declaredLean 4.32.0

Antichain operator

antichain_operator

Plain-language statement

For an antichain A\mathfrak{A} of pairwise incomparable tiles, and measurable functions ff and gg bounded by the indicators of FF and GG, the pairing of gg with the Carleson sum over A\mathfrak{A} is controlled by the L2L^2 norms of ff and gg and by positive powers of the two tile-density parameters. Concretely, the bound is

C(a,q)dens1(A)(q1)/(8a4)dens2(A)1/q1/2f2g2.C(a,q)\,\mathrm{dens}_1(\mathfrak{A})^{(q-1)/(8a^4)}\,\mathrm{dens}_2(\mathfrak{A})^{1/q-1/2}\,\lVert f\rVert_2\lVert g\rVert_2.

harmonic analysisFourier analysismeasure theory

Source project: Carleson formalization

Person-level attribution pending.

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