Stein, Erwin. “Milestones of Direct Variational Calculus and Its Analysis from the 17th Century until Today and Beyond – Mathematics Meets Mechanics – With Restriction to Linear Elasticity”. Computer Assisted Methods in Engineering and Science 25, no. 4 (July 2, 2019): 141–225. Accessed January 18, 2026. https://cames.ippt.gov.pl/index.php/cames/article/view/256.