2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/221117We prove new formulae for the wave operators for a Friedrichs scattering system with a rank one perturbation, and we derive a topological version of Levinson's theorem for this model.7 pagesMathematical Physics46N50; 81Q10; 35Q40; 47L90text