2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/37633The universality of single-spin asymmetry on inclusive $π$-meson production is discussed. This universality can be related to the hadron substructure -- constituent quarks in the frame of the quark model for U-matrix.4 pages, 3 figures, Presented on X International Workshop on High Energy Spin Physics (SPIN-03), Dubna, September 16-20High Energy Physics - Experimenttext