Friedrichs and Kre\u{\i}n type extensions in terms of representing maps
Friedrichs and Kre\u{\i}n type extensions in terms of representing maps
A semibounded operator or relation $S$ in a Hilbert space with lower bound $m \in {\mathbb R}$ has a symmetric extension $S_{\rm f}=S {\, \widehat + \,} (\{0\} \times {\rm mul\,} S^*)$, the weak Friedrichs extension of $S$, and a selfadjoint extension $S_{\rm F}$, the Friedrichs extension of $S$, that …