of Partial Differential Equations
www.jstor.org › stable › pdfof Partial Differential Equations AVNER FRIEDMAN Communicated by Ε. Hopf Introduction. Interior estimates for second order elliptic equations have been derived by J. Schauder [8][9], More recently A. Douglis & L. Nirenberg [2] have extended these estimates to elliptic systems of great generality. Their