A relaxation result in the vectorial setting and $L^p$-approximation for $L^infty$-functionals

We provide relaxation for not lower semicontinuous supremal functionals of the type $W^{1,infty}(Omega;mathbb R^d) i u mapstosupess_{ x in Omega}f( abla u(x))$ in the vectorial case, where $Omegasubset mathbb R^N$ is a Lipschitz, bounded open set, and $f$ is level convex. The connection with indicator functionals is also enlightened, thus extending previous lower semicontinuity results in that framework. Finally we discuss the $L^p$-approximation of supremal functionals, with non-negative, coercive densities $f=f(x,xi)$, which are only $L^N otimes B_{d times N}$-measurable.