COSTANDIN, Marius, Petru DOBRA, and Bogdan GAVREA. “A New Proof of Ackermann’s Formula from Control Theory”. Studia Universitatis Babeș-Bolyai Mathematica 62, no. 3 (September 30, 2017): 325–329. Accessed February 5, 2025. https://studia.reviste.ubbcluj.ro/index.php/subbmathematica/article/view/1838.