The one-term, 4-hours-a-week course on magnetism presented a chal-lenge known to all physicists in the field: research interests in the past half a century have been dominated by the effects of strong electron-electron interaction, while standard solid state physics textbooks re-main within the bounds of band theory which is a suitable language for weakly correlated systems, and then add a chapter on Heisenberg magnets whose very existence is in contradiction with the rest of the material, and gets never properly justified. The usual way of clarifying these matters is to go through a formal education in many-body theory, and to learn about strong correlation effects piecemeal from its applica-tions (and breakdowns). This, however, is usually the beginning of the professional career of a theoretician, and it may not be the most recom-mendable approach for others, One takes a long time to discover that there is a unified, non-formal way of thinking about strong correlation phenomena that has long been shared by experimentalists and theoreti-cians in the field; it can be called elementary and should be accessible to all - but it cannot be found in the well-known textbooks.
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