semi-angle $\alpha$, $\alpha \in [0,\pi/2)$. Then there exists a unique maximal sectorial relation $H$ in $\sH$ with vertex at the origin and semi-angle $\alpha$ in $\sH$ such that $$\label{glij}
\dom H \subset \dom \st,$$ and for every $\{ h,h' \} \in H$ and $k \in \dom \st$ one has $$\label{eqn:firstrepresentation}
 \st[h,k] = ( h', k ).$$ Conversely, for every maximal sectorial relation $H$ with vertex at the origin and semi-angle $\alpha$, $\alpha \in [0,\pi/2)$, there exists a unique closed sectorial form $\st$ such that and are satisfied.

This result contains as a special case the connection between nonnegative selfadjoint relations and closed nonnegative forms. The nonnegative selfadjoint relation $H_r$ corresponding to the real part $\st_{\r}$ of the form $\st$ is called the real part of $H$; this notion should not to be confused with the real part introduced in [@HSnSz09].\
In the theory of sectorial operators one encounters expressions $T^{*}(I+iB)T$ where $T$ is a linear operator from a Hilbert space $\sH$ to a Hilbert space $\sK$ and $B \in \mathbf{B}(\sK)$ is a selfadjoint operator. In the context of sectorial relations the operator $T$ may be replaced by a linear relation $T$. A frequently used observation is that when $T$ is 