Şerb, Ioan. “On a Modified Modulus of Smoothness of a Banach Space”. Rev. Anal. Numér. Théor. Approx. 22, no. 2 (August 1, 1993): 217–225. Accessed November 25, 2024. https://ictp.acad.ro/jnaat/journal/article/view/1993-vol22-no2-art12.