On Backlund transformations for some second-order nonlinear differential equationsWe obtain
second-order nonlinear differential
equations (and the associated Backlund
GRADIENT ESTIMATE FOR SOLUTIONS OF SECOND-ORDER ELLIPTIC EQUATIONSGRADIENT ESTIMATE FOR SOLUTIONS OF
SECOND-ORDER ELLIPTIC
EQUATIONS On direct variational formulations for second order evolutionary equationsOn direct variational formulations for
second order evolutionary
equations Inner uniqueness theorem for second order linear elliptic equation with constant coefficients of
second order, and prove that it vanishes if zeros of f condense to two points along non-collinear rays