1. Modified Krein formula and analytic perturbation procedure for scattering on arbitrary junction;Adamyan,2009
2. Theory of Linear Operators in Hilbert Space. Vol. II;Akhiezer,1981
3. Essential spectrum for Maxwell's equations;Alberti;Ann. Henri Poincaré,2019
4. Sobolev Spaces on Domains;Burenkov,1998