A note on dyadic coverings and nondoubling Calderón–Zygmund theory

We construct a family of n + 1 dyadic filtrations in R n , so that every Euclidean ball B is contained in some cube Q of our family satisfying diam ( Q ) ≤ c n diam ( B ) for some dimensional constant c n . Our dyadic covering is optimal on the number of filtrations and improves previous results of Christ and Garnett/Jones by extending a construction of Mei for the n -torus. Based on this covering and motivated by applications to matrix-valued functions, we provide a dyadic nondoubling Calderón–Zygmund decomposition which avoids Besicovitch type coverings in Tolsa’s decomposition. We also use a recent result of Hytönen and Kairema to extend our dyadic nondoubling decomposition to the more general setting of upper doubling metric spaces.