Глушко В. Н.
Укр. мат. журн. - 1994. - 46, № 5. - С. 475–483
The problem of uniqueness of the best approximations in the space $L_1[a, b]$ is studied We consider the problem of the best approximation and the best $(\alpha, \beta)$-approximation of continuous functions and the problem of the best one-sided approximation of continuously differentiable functions.