Collatz, L. “Verkettete Und Freie Approximation Bei Differentialgleichungen: Chained and Free Approximation for Differential Equations”. Rev. Anal. Numér. Théorie Approximation 3, no. 2 (August 1, 1974): 151–160. Accessed November 23, 2024. https://ictp.acad.ro/jnaat/journal/article/view/1974-vol3-no2-art4.