Counterexample to boundary regularity of a strongly pseudoconvex CR submanifold: An addendum to the paper of Harvey-Lawson. Luk, Hing Sun; Yau, Stephen S.-T. — 1998 Annals of Mathematics. Second Series
Normalization of Differential Equations Defining a CR Structure. Hing-Sun Luk — 1978 Inventiones mathematicae