Removable sets for solutions of the Euler equations (Q1103102)

\textit{L. I. Hedberg} [Ark. Mat. 12, 181-201 (1974; Zbl 0297.30017)] characterized removable sets for the class \(HD^ p\) of harmonic functions u with \(\int | \nabla u|^ p dx<\infty\) and for the subclass \(FD^ p\) of these functions with vanishing flux. The author introduces analogous classes \(HD^ p\) and \(KD^ p\) relevant to the Euler equation for the variational integral \(\int \psi (x,\nabla u)dx\) and show (under certain conditions on \(\psi)\) that removable sets for \(HD^ p\) \((KD^ p)\) are the same as for \(HD^ q\) \((FD^ q)\) where \(q=p/(p-1)\), \(p\geq 2\). A geometric characterization of removable sets \((NED_ p\)-sets) is mentioned either.