2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/53955We dicuss functorial consequences of way the eta invariant of Dirac operators behaves under gluing and change of boundary conditions.pages10, Latex, reportSFB288-93High Energy Physics - TheoryThe $η$-Invariant as a Lagrangian of a Topological Quantum Field Theorytext