A Local Lewy Theorem for $p$-Harmonic Function with Non-zero Gradient in $R^3$

Abstract

We establish a local Lewy-type theorem for \(p\)-harmonic function with non-zero gradient in dimension three space $R^3$. Let \(1<p<\infty\), and let \(u\in W^{1,p}_{\mathrm{loc}}(Ω)\) be a weak \(p\)-harmonic function in a domain \(Ω\subset\mathbb R^3\), assume it satisfies \(|Du|>0\), we prove that a locally homeomorphic gradient map \(Du\) must have non-vanishing Hessian determinant. Hence \(Du\) is a local diffeomorphism.