... Ω,thenΩkθ|∇u|r−2 βx|∇u|r0−2∇u ·∇ϕdx≥ 03.15 for all nonnegative ϕ ∈ H1,r0Ω.Proof. Let ϕ ∈ H1,r0Ω and choose nonnegative sequence φi∈ C∞0Ω such that ϕi→ ϕ inH1,rΩ. ... Heinonen, T. Kilpel¨ainen, and O. Martio, Nonlinear Potential Theory of Degenerate Elliptic Equations,Oxford Mathematical Monographs, The Clarendon Press, Oxford University Press, New York, NY,USA, ... from a nonlinear slip condition of Navier type.Similar derivations based on the Navier slip condition occur elsewhere, for example, 8, 9,10, equation 2.4.The mathematical model for this...