[1] W. W. Breckner, Bruno Brosowski: Ein kriterium zur charakterisierung von sonnen. Mathematika 13 (1971), 181 -188. MR 0342935

[2] P. Govindarajulu, D. V. Pai: On properties of sets related to f-projections. J. Math. Anal. Appl., 73 (1980), 457-465. MR 0563996 | Zbl 0476.46012

[3] A. F. Monna: Remarks on some problems in linear topological spaces over fields with non-archimedean valuation. Proc. Kon. Ned. Akad. Wetensch., A 71 (1968), 484-496. MR 0247411

[4] T. D. Narang: Characterizations of elements of best approximation in non-archimedean normed spaces. Arch. Math., 20 (1984), 10-12. MR 0817554

[5] T. D. Narang: On f-best approximation in topological spaces. To appear in Arch. Math. MR 0833135 | Zbl 0585.41029

[6] T. D. Narang, S. K. Garg: Best approximation in nonarchimedean normed spaces. Math. Forum, 5 (1982), 29-32.

[7] T. D. Narang, S. K. Garg: On f-farthest points of sets. Communicated.

[8] D. V. Pai, P. Veermani: Applications of fixed point theorems to problems of optimization and best approximation. Non-linear Analysis and Applications, Marcel Dekker, Inc. New York, Edited by S. P. Singh and J. H. Burry (1982), 393-400.