“…Street [Str17] later studied the boundedness in Sobolev spaces of the "multi-parameter" singular Radon transforms. Some other related works include [NRSW12], [RS92], [MRS95], [VW20], [Gre16], [BT13], [Wan20], [Vit17], [She18], [Roo17], [LSY20], [LY18], [Hu20], [HL18], [GHLR17], [Guo17b], [Guo15b], [Guo17a], [Guo15a], [DLZ19], [DL20], [Chr20], [CL18], [Ou17], [DPP18], [Bat13], [APP19], [PS97], [BLMW18], [CHKY08], [FGW08], [Var76], [SW78], [NRS01], [ZK19], [Lie20], [Gre07a], [Hel66], [Gre01b], [Gre01a], [NRW76], [TW03], [PS86], [See98], [Sto11], [Sto14], [Gre19b], ...…”