Abstract. We establish local to global results for a function space which is larger than the well known BMO space, and was also introduced by John and Nirenberg.
IntroductionThe space of functions of bounded mean oscillation, abbreviated to BMO, is introduced by John and Nirenberg [12]. In the same paper, John and Nirenberg introduced a larger space of functions. As opposed to any BMO function, that has exponentially decaying distribution function, a function in this larger space is known to belong to a weak L p -space, [12, Lemma 3]; the inclusion being strict, see [1, Example 3.5]. We extend this weak-type inequality to the case of John domains. The equivalence of local and global BMO norms is a rather well-known result, due to Reimann and Rychener [17]. We obtain the corresponding local to global result for the mentioned larger space of functions.Let G be a proper open subset of R n , n ≥ 1. The following condition was introduced in [12]: Let f : G → R be a function in L 1 (G) and let us assume that there exists 1 < p < ∞ such thatwhere the supremum is taken over all partitions P(G) of G into cubes such that Q ⊂ G for each Q ∈ P(G), the interiors of these cubes are pairwise disjoint, and G = Q∈P(G) Q. We call such partitions admissible. It is shown in [12, Lemma 3] that a function satisfying (1.1), with G being a cube Q in R n , belongs to a weak L p (Q)-space. More precisely, there exists a positive constant C, depending only on n and p, so that for all f ∈ L 1 (Q),We refer to [7,19,1] for other proofs of this result.We mention papers [5,6,15,16] where a related discrete summability condition is studied, and a recent paper [2] where its relation to condition (1.1) is discussed. In [5], in particular, the authors prove a local to global result in connection with this discrete summability condition.