참고문헌
- Duke Math. v.10 A note on local solvability C. Hoel
- Linear Particl Differential Operators L. Hormander
- Israel J. Math v.9 An unsolvable hypoelliptic differential operator Y. Kannai
- Comm. Pure Appl. Math. v.23 On local solvability of linear partial defferential equations, Part 1 : Necessary conditions, Part 2 : Suffricient conditions C. Nirenberg;F. Treves
- Bull. of Korean Math. Soc. v.31 Unsolvable partial differential operators of degeneratetype R. J. Kim;J. S. Kim
- Comm. Pure Appl. Math. v.24 Analytic-hypoelliptic particl differential equations of principle type F. Treves