A Chebyshev type alternation theorem for best approximation by a sum of two algebras

Aida Asgarova, Ali Huseynli, Vugar Ismailov

Let $X$ be a compact metric space, $C(X)$ be the space of continuous real-valued functions on $X$, and $A_1$, $A_2$ be two closed subalgebras of $C(X)$ containing constant function…