On the Palais principle for non-smooth functionals

Original · EN

If G is a compact Lie group acting linearly on a Banach space X and f is a G-invariant function on X, we provide new versions of the so-called Palais' criticality principle for f:X→, in the framework of non-smooth critical point theory. We apply the results to a class of PDEs associated with functionals which are merely lower semi-continuous and could not be treated by previous versions of the principle.