BEST APPROXIMATION AND BEST BIAPPROXIMATION BY CLOSED UNIT BALLS

We obtain a cofficint and nesessery theoreom simple for compactness and weakly compactness of the best approximate sets by closed unit balls. Also we consider relation Kadec-Klee property and schur property with this objects. These theorems are extend of papers mohebi and Narayana. In this paper we introduce best biapproximation and obtain some important theorems. Also we define biorthogonality two points to one point and introduce ellipse neighborhood