Vaupel, J.W. <https://pure.iiasa.ac.at/view/iiasa/2478.html>  (1986).  How Change in Age-specific Mortality Affects Life Expectancy.   Population Studies 40 (1) 147-157. 10.1080/0032472031000141896 <https://doi.org/10.1080/0032472031000141896>.