@article {2017,
	title = {Krein-Visik-Birman self-adjoint extension theory revisited},
	number = {SISSA;25/2017/MATE},
	year = {2017},
	abstract = {The core results of the so-called KreIn-Visik-Birman theory of
self-adjoint extensions of semi-bounded symmetric operators are reproduced,
both in their original and in a more modern formulation, within a
comprehensive discussion that includes missing details, elucidative steps,
and intermediate results of independent interest.},
	url = {http://preprints.sissa.it/handle/1963/35286},
	author = {Matteo Gallone and Alessandro Michelangeli and Andrea Ottolini}
}
