Martí Prats: Weak reverse Hölder inequalities for doubling measures

Let μ be a doubling Radon measure in Rd with support X. We prove a local and quantitative form of the Bennewitz–Lewis theorem in this setting: if a Radon measure ν satisfies the Bennewitz–Lewis condition on a bounded relatively open set V⊂X with a small enough constant, then ν|V≪μ|V and its density satisfies a reverse Hölder inequality on every compact subset K⊂V. Along the way we develop the dyadic toolkit these arguments run on — triple cubes defined through neighbours, the basis D∪3D, and a Whitney decomposition — and we collect the Muckenhoupt-type classes of weights over that basis. The same machinery yields a local Gehring lemma for enlarged balls: both theorems are deduced from a single bootstrapping lemma, stated once for p=1 and p>1.