1. Entire functions, in the classification of differentiable germs tangent to the identity, in one or two variables;Ahern;Trans. Amer. Math. Soc.,1995
2. A.P. Bergamasco, A. Meziani, Semiglobal solvability of a class of planar vector fields of infinite type, VI Workshop on Partial Differential Equations, Part I, Rio de Janeiro, 1999; Mat. Contemp. Vol. 18 (2000) pp. 31–42.
3. Analytic form of differential equations;Brjuno;Trans. Moscow Math. Soc.,1971
4. L. Hörmander, The analysis of linear partial differential operators, I and IV. Grundlehren der Mathematischen Wissenschaften (Fundamental Principles of Mathematical Sciences), Vol. 256, 275. Springer, Berlin, 1983, 1985.
5. Local solvability of first order linear operators with Lipschitz coefficients;Hounie;Duke Math. J.,1991