2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/97275We consider O(3) sigma-model as a reduction of the principal chiral field. This approach allows to introduce the currents with ultralocal Poisson brackets and to obtain the zero-curvature equation which admits the fundamental Poisson bracket.Uppsala University preprint, 12 pages, LaTeX fileHigh Energy Physics - Theorytext