2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/59178C.M. Ringel defined Hall algebra associated with the category of representations of a quiver of Dynkin type and gave an explicit description of the structure constants of the corresponding Lie algebra. We utilize functorial properties of the Hall algebra to give a simple proof of Ringel's result, and to generalize it to the case of a quiver of affine type.48 pagesRepresentation Theorytext