We introduce the iterated commutator for the Riesz transforms in the multiparameter
flag setting, and prove the upper bound of this commutator with respect to the symbol
in the
flag BMO space. Our methods require the techniques of semigroups, harmonic
functions and multiparameter flag Littlewood–Paley analysis. We also introduce the
big commutator in this multiparameter flag setting and prove the upper bound with
symbol
in the flag little bmo space by establishing the “exponential-logarithmic”
bridge between this flag little bmo space and the Muckenhoupt
weights with flag structure. As an application, we establish the div-curl
lemmas with respect to the appropriate Hardy spaces in the multiparameter
flag setting.
Keywords
multiparameter flag setting, flag commutator, Hardy space,
BMO space, div-curl lemma