2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/22019Increasing every year the retirement age by the same amount as the increase of the life expectancy gives roughly stable ratios of the number of retired to working-age people in industrialized countries. Continuous influx of immigrants, below one percent per year of the total population, is needed for this stabilization.6 pages including 4 figuresStatistical MechanicsPopulations and Evolutiontext