. . "elliptic partial differential operator" . "Elliptic" . . "elliptic equations" . "ellipticity condition" . "elliptic partial differential equation" . "nonlinear elliptic systems" . . . "Elliptic partial differential equation" . . "Elliptic partial differential equations" . "Theory of elliptic partial differential equations" . . "Elliptic partial differential equation" . "theory of elliptic partial differential equations" . "elliptic differential equation" . "elliptic equation" . . . "second-order elliptic partial differential equations" . "elliptic PDEs" . . . . . . . . "elliptic" . .