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Extremal extensions for the sum of nonnegative selfadjoint relations
The sum $A+B$ of two nonnegative selfadjoint relations (multi-valued operators) $A$ and $B$ is a nonnegative relation. The class of all extremal extensions of the sum $A+B$ is characterized as products of relations via an auxiliary Hilbert space associated with $A$ and $B$. The so-called form sum extension of $A+B$ …