Gallone, MatteoMichelangeli, Alessandro2020-03-272020-03-272020https://openscience.sissa.it/handle/1963/35347We produce a simple criterion and a constructive recipe to identify those self-adjoint extensions of a lower semi-bounded symmetric operator on Hilbert space which have the same lower bound as the Friedrichs extension. Applications of this abstract result to a few instructive examples are then discussed.enFunctional AnalysisMathematical PhysicsPreprint