Crstici, B., and O. Lipovan. “A Probabilistic Approach to the Integrability Concept”. Anal. Numér. Théor. Approx. 17, no. 2 (August 1, 1988): 93–98. Accessed May 18, 2024. https://ictp.acad.ro/jnaat/journal/article/view/1988-vol17-no2-art1.