Mustăţa, Costică. “Some Remarks Concerning Norm Preserving Extensions and Best Approximations”. Rev. Anal. Numér. Théor. Approx. 29, no. 2 (August 1, 2000): 173–180. Accessed March 28, 2024. https://ictp.acad.ro/jnaat/journal/article/view/2000-vol29-no2-art7.