Solutions of Vectorial Hamilton-Jacobi Equations are Rank-One Absolute Minimisers in $L^\infty$

Given the supremal functional $E_\infty(u,\Omega')=ess\,\sup_{\Omega'} H(\cdot,D u)$ defined on $W^{1,\infty}_{loc}(\Omega,\mathbb{R}^N)$, $\Omega' \Subset \Omega\subseteq \mathbb{R}^n$, we identify a class of vectorial rank-one Absolute Minimisers by proving a statement slightly stronger than the next claim: vectorial solutions of the Hamilton-Jacobi equation $H(\cdot,D u)=c$ are rank-one Absolute Minimisers if they are $C^1$. Our minimality notion is a generalisation of the classical $L^\infty$ variational principle of Aronsson to the vector case and emerged in earlier work of the author. The assumptions are minimal, requiring only continuity and rank-one convexity of the level sets.