A Pontryagin's Principle for Boundary Control Problems of Quasilinear Elliptic Equations

Recently, Casas and Yong [14] proved a Pontryagin's principle for pointwise stateconstrained control problems governed by elliptic quasilinear equations. There, the key point of the proof was a Lieberman's result [23] about the boundedness of the gradient of the state. It was possible to use this result because the control was distributed in the domain.