Ripeanu, D. “Sur Un opérateur Qui Conserve l’allure d’une Fonction: On an Operator That Preserves the Shape of a Function”.
Rev. Anal. Numér. Théorie Approximation 2 (February 1, 1973): 105–112. Accessed April 11, 2025.
https://ictp.acad.ro/jnaat/journal/article/view/1973-vol2-art11.