of an accretive relation is also accretive. An accretive relation $H$ in $\sH$ is said to be *maximal accretive* if the existence of an accretive relation $H'$ in $\sH$ with $H \subset H'$ implies $H' = H$. A maximal accretive relation is automatically closed. In a similar way, a linear relation $H$ in a Hilbert space $\sH$ is said to be *sectorial* with vertex at the origin and semi-angle $\alpha$, $\alpha \in [0,\pi /2)$, if $$\label{sect0-}
 | \IM (h',h) | \le (\tan \alpha) \,\RE (h',h),
 \quad  \{ h, h'\} \in H.$$ The closure of a sectorial relation is also sectorial. A sectorial relation $H$ in a Hilbert space $\sH$ is said to be *maximal sectorial* if the existence of a sectorial relation $H'$ in $\sH$ with $H \subset H'$ implies $H' = H$. A maximal sectorial relation is automatically closed. Note that a sectorial relation is maximal sectorial if and only if it is maximal as an accretive relation; see [@HSnSz09].

A sesquilinear form $\st=\st[\cdot, \cdot]$ in a Hilbert space $\sH$ is a mapping from $\dom \st \subset \sH$ to $\dC$ which is linear in its first entry and antilinear in its second entry. The adjoint $\st^{*}$ is defined by 