[1] AMIR D., DEUTSCH F.: Suns, moons and quasi-polyhedra. J. Approximation Theory 6 (1972), 176-201. MR 0364982 | Zbl 0238.41014

[2] BLATTER J., MORRIS P. D., WULBERT D. E.: Continuity of the set-valued metric projection. Math. Ann. 178 (1968), 12-24. MR 0228984 | Zbl 0189.42904

[3] BROWN A. L.: Best $n$-dimensional approximation to sets of functions. Proc. London Math. Soc. 14 (1964), 577-594. MR 0167761 | Zbl 0129.04702

[4] CLAUSING A., PAPADOPOULOU S.: Stable convex sets and extremal operators. Math. Ann. 231 (1978), 193-203. MR 0467249 | Zbl 0349.46002

[5] DAY M. M.: Normed linear spaces. Springer Verlag Berlin - Heidelberg - New York 1973 (third ed.). MR 0344849 | Zbl 0268.46013

[6] HARAZIŠVILI A. B.: On the locally conic sets. (in Russian), Soobšč. Akad. Nauk Gruzin. SSR 80 (1975), 29-32. MR 0397543

[7] WEGMANN R.: Some properties of the peak-set-mapping. J. Approximation Theory 8 (1973), 262-284. MR 0352834 | Zbl 0264.41021