Precupanu, Teodor. “On a Dual Characterisation in Best Approximation Problem”. Rev. Anal. Numér. Théor. Approx. 37, no. 2 (August 1, 2008): 191–196. Accessed April 25, 2024. https://ictp.acad.ro/jnaat/journal/article/view/2008-vol37-no2-art11.