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Hardy and Littlewood: controlling the largest local averages

Contribution grade

Harmonic analysis / maximal operators · Exact theorem and reusable mathematical method

Reference score380,000Provisional editorial estimate of this exact contribution; its grade is assessed separately.

What changed

An average can hide a short burst. What if one looks around every point and chooses the interval with the largest average? Hardy and Littlewood show how to control these maximal averages in one dimension. Their rearrangement comparisons lead to an Lp norm bound p/(p−1) for the one-sided average, when p is greater than one. For their two-direction endpoint-interval maximal function, the corresponding integral bound is twice that factor raised to p. A finite-interval endpoint result also explains why an extra logarithmic integrability condition can control the maximal average when ordinary integrability alone cannot.

Scientific scope

An average can hide a short burst. What if one looks around every point and chooses the interval with the largest average? Hardy and Littlewood show how to control these maximal averages in one dimension. Their rearrangement comparisons lead to an Lp norm bound p/(p−1) for the one-sided average, when p is greater than one. For their two-direction endpoint-interval maximal function, the corresponding integral bound is twice that factor raised to p. A finite-interval endpoint result also explains why an extra logarithmic integrability condition can control the maximal average when ordinary integrability alone cannot. These are the original one-dimensional interval averages, not arbitrary-dimensional or weighted maximal theorems. The sharp factor two in the rearrangement comparison is not asserted to be the optimal strong Lp constant. The L log L endpoint requires a finite interval; there is no general strong L1 bound here. Toeplitz-style rearrangement and prior Hardy, Elliott and Young inputs are distinct. The paper credits T. W. Chaundy for the substance of Lemma6 proof without making him an article coauthor.

Evidence

The linked original works support the scoped statement and contribution attribution. WRS has not independently replayed experiments or reconstructed a full mathematical proof. These are the original one-dimensional interval averages, not arbitrary-dimensional or weighted maximal theorems. The sharp factor two in the rearrangement comparison is not asserted to be the optimal strong Lp constant. The L log L endpoint requires a finite interval; there is no general strong L1 bound here. Toeplitz-style rearrangement and prior Hardy, Elliott and Young inputs are distinct. The paper credits T. W. Chaundy for the substance of Lemma6 proof without making him an article coauthor.

Contributors

Provisional WRS assessment, edition 2026-10-23.7. Independent expert calibration is pending. This grade does not certify correctness or assign ownership.

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