1. Bernstein, I. N.: The analytic continuation of generalized functions with respect to a parameter. Functional Anal. Appl.6, 26?40 (1972)
2. Bernstein, I. N., Gelfand, S. I.: Meromorphy of the functionP ?. Functional Anal. Appl.3, 84?86 (1969)
3. Björk, J. E.: Dimensions over Algebras of Differential Operators. Preprint
4. Kashiwara, M.: Algebraic study of systems of partial differential equations. Master's thesis, Univ. of Tokyo, 1971 (Japanese)
5. Kashiwara, M.: On the maximally overdetermined system of linear differential equations. I. Publ. RIMS, Kyoto Univ.10, 563?579 (1975)