Vishik, M. I.; Grushin, V. V. Degenerating elliptic differential and pseudo-differential operators. (English) Zbl 0222.35024 Russ. Math. Surv. 25, No. 4, 21-50 (1970). MSC: 35J70 35S99 PDF BibTeX XML Cite \textit{M. I. Vishik} and \textit{V. V. Grushin}, Russ. Math. Surv. 25, No. 4, 21--50 (1970; Zbl 0222.35024) Full Text: DOI OpenURL
Vishik, M. I.; Grushin, V. V. Entartende elliptische Differential- und Pseudodifferentialoperatoren. (Russian) Zbl 0209.40901 Usp. Mat. Nauk 25, No. 4(154), 29-56 (1970). MSC: 35S05 35J70 PDF BibTeX XML Cite \textit{M. I. Vishik} and \textit{V. V. Grushin}, Usp. Mat. Nauk 25, No. 4(154), 29--56 (1970; Zbl 0209.40901) OpenURL