2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/87700We illustrate the use of the invariant spin field for describing permissible equilibrium spin distributions in high energy spin polarised proton beams.}3 pages with 2 embedded figures. Latex. Paper 3 of a set of 5. others are physics/9901038 physics/9901041 physics/9901043 physics/9901044Accelerator PhysicsClassical PhysicsQuantum Physicstext