“…The boundedness and compactness of [b, I α ] i on variant function spaces have been the topic in many articles recently, see [1,2,3,5,6,12,13,17,18,19,26], among numerous references. One of the interesting questions on [b, I α ] i is whether it can be used to characterize BM O(R n ) by boundedness, or CM O(R n ) by compactness, as those in the linear setting (see [7,9,27] etc). Recently, Chaffee [5] established the following result.…”