"Version: 20230501"--Title page verso.Includes bibliographical references.1. Introduction -- 1.1. Topological insulators -- 1.2. Topological semimetals -- 1.3. Collective excitations in magnets2. Topological band theory -- 2.1. Topological invariants -- 2.2. The Su-Schrieffer-Heeger model -- 2.3. The Haldane model3. Basics of magnons -- 3.1. Magnon dispersion relation -- 3.2. Magnon excitation …