1. M. S. Baouendi, C. H. Chang, F. Treves.Microlocal Hypo-Analytic and Extension of CR Functions, J. Differ. Geom., 18 (1983), 331-391.
2. M. S. Baouendi and F. Treves, A local constancy principle for the solutions of certain overdetermined systems of first-order linear partial differential equations, in Advances in Mathematics Supplementary Studies, Academic Press, New York, (1981), 245-262.
3. S. Berhanu, P. D. Cordaro and J. Hounie, An introduction to involutive structures, New mathematical monographs, University Press, (2008).
4. P. D. Cordaro, Resolubilidade das Equações Diferenciais Parciais Lineares, Matemática Universitária, 14, (1992), 51-67.
5. P. D. Cordaro, Sistemas de Campos Vetoriais Complexos, Instituto de matemática pura e aplicada, (1986).