Rearrangement estimates and limiting embeddings for anisotropic Besov spaces

The paper is dedicated to the study of embeddings of the anisotropic Besov spaces $B_{p;{\theta }_1,\mathrm{.}\mathrm{.}\mathrm{.},{\theta }_n}^{{\beta }_1,\mathrm{.}\mathrm{.}\mathrm{.},bet{a}_n}({\mathbb{R}}^n)$ into Lorentz spaces. We find the sharp asymptotic behaviour of embedding constants when some of the exponents ${\beta }_k$ tend to 1 (${\beta }_k<1)$. In particular, these results give an extension of the estimate proved btý Bourgain, Brezis, and Mironescu for isotropic Besov spaces. Also, in the limit, we obtain a link with some known embeddings of anisotropic Lipschitz spaces. One of the key results of the paper is an anisotropic type estimate of rearrangements in terms of partial moduli of continuity.