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A maximum principle for weakly coupled systems of second order partial differential equations with nonnegative characteristic form
The maximum principle of Fichera for a single second order partial differential equation with nonnegative characteristic form is extended to weakly coupled linear systems of such equations.A Phragmen-Lindelöf principle for such systems, giving conditions for the maximum principle to hold in unbounded domains, is proved.Comparison theorems for degenerate parabolic semilinear …