S. N. BERNSHTEIN'S Contribution to the Theory of Partial Differential Equations Akhiezer, N. I. ; Petrovskii, I. G. Abstract Publication: Russian Mathematical Surveys Pub Date: April 1961 DOI: 10.1070/RM1961v016n02ABEH004101 Bibcode: 1961RuMaS..16....1A