Sameness of age cohorts in the mathematics of population growth.

"Considering age groups as part of cohorts, implicit in LLM [a Leslie-Lotka finitist model], causes difficulty, manifested by the extensionality paradox. The proposition made here was that cohorts are empirical temporal entities, while age groups are theoretical entities, references only. Cohort is a multitude of persons born at the same time interval, throughout the totality of their lives. Age group, on the other hand, is a concept only, constituted by the notion of the age interval....A model of household and population growth based on the household composition matrix yields results that are inherently different from these of LLM."