Raşa, Ioan. “Determining Sets for Finitely Defined Operators”. Anal. Numér. Théor. Approx. 10, no. 1 (February 1, 1981): 89–93. Accessed April 14, 2025. https://ictp.acad.ro/jnaat/journal/article/view/1981-vol10-no1-art10.