M-Accretive Realisations of Skew-Symmetric Operators

We consider skew-symmetric operators $A_0$ on a Hilbert space $H$ and characterise all (nonlinear) m-accretive restrictions of $A:=-A_0^{\ast }$ in terms of the “deficiency spaces” $\ker (1\pm A)$. The results are illustrated by several examples and applied to a partial differential equation with an impedance type boundary condition.