Narang, T. and Gupta, S. (2016) “BEST APPROXIMATION AND BEST COAPPROXIMATION IN METRIC LINEAR SPACES”, Journal of Nonlinear Analysis and Optimization: Theory & Applications (JNAO), 7(1), pp. 137–143. available at: https://ph03.tci-thaijo.org/index.php/jnao/article/view/2819 (accessed: 2 September 2026).