Works citing   [J. Math. Anal. Appl. 446 (2017), 1328-1355]

1. J. Behrndt, M. Langer, V. Lotoreichik and J. Rohleder:
   Spectral enclosures for non-self-adjoint extensions of symmetric operators,
   J. Funct. Anal. 275 (2018) 1808-1888.