Michelangeli, Alessandro2016-02-232016-02-232015-12-02https://openscience.sissa.it/handle/1963/35174The core results of the so-called Krein-Vishik-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.enSelf-adjoint operators, self-adjoint extensions, von Neumann extension theory, Krein-Vishik-Birman extension theoryPreprintMAT/0759/2015/MATE