# Atomic decompositions, two stars theorems, and distances for the Bourgain-Brezis-Mironescu space and other big spaces

## TL;DR

This paper establishes duality and atomic decompositions for a class of Banach spaces, including the Bourgain-Brezis-Mironescu space, and provides formulas for distances within these spaces.

## Contribution

It proves that certain Banach spaces are dual spaces, offers atomic decompositions of their preduals, and applies these results to the Bourgain-Brezis-Mironescu space.

## Key findings

- Proves duality of the space $E$ with a supremum-type norm.
- Provides atomic decomposition of the predual space.
- Derives a formula for the distance from an element to a subspace.

## Abstract

Given a Banach space $E$ with a supremum-type norm induced by a collection of operators, we prove that $E$ is a dual space and provide an atomic decomposition of its predual. We apply this result, and some results obtained previously by one of the authors, to the function space $\mathcal{B}$ introduced recently by Bourgain, Brezis, and Mironescu. This yields an atomic decomposition of the predual $\mathcal{B}_\ast$, the biduality result that $\mathcal{B}_0^\ast = \mathcal{B}_\ast$ and $\mathcal{B}_\ast^\ast = \mathcal{B}$, and a formula for the distance from an element $f \in \mathcal{B}$ to $\mathcal{B}_0$.