2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/177664We review different definitions of the $ε'$ parameter describing direct CP violation in neutral kaon decays, which was precisely measured in recent experiments, and point out the inconsistency of some of them due to a CPT constraint. The proper comparison of the experimental results to the theoretical computations is discussed.9 pages, 1 figureHigh Energy Physics - Phenomenologytext