Differential equations which have no solutions
In Chapter III we proved that a differential equation with constant coefficients can be solved for an arbitrary right-hand side f, at least in relatively compact open subsets of the open set where f is defined. It was discovered rather recently by H. Lewy  that the situation is completely different when the coefficients are variable.
KeywordsDifferential Operator Variable Coefficient Order Differential Operator Linear Partial Differential Operator Real Symmetric Matrix
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