2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/139962It is shown that the Tsallis entropies are the only entropies of the form $H(P)=-\sum_i f(p_i)$, with suitable assumptions on $f$, satisfying the condition of composability.7 pages, updated references and introduction / discussion sections. Main text remains unchangedStatistical Mechanicstext