2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/54885New features of systems with non-trivial topology such as fractional quantum numbers, inequivalent quantizations, good operators, topological anomalies, etc. are described in the framework of an algebraic quantization procedure on a group. Modular invariance naturally appears as a subgroup of good operators in the particular case of the torus.Latex, 5 pages with no figures. Uses style file group21.sty Contribution to the XXI International Colloquium on Group Theoretical Methods in Physics, Goslar, GermanyHigh Energy Physics - Theorytext