1. A remark on metric spaces;Artémiadis;Proc. Kon. Ned. Akad. van Wetensch,1965
2. Les espaces métriques quasiconvexes;Blanc;Ann. Sci. Ecole norm. sup., III Ser,1938
3. Untersuchungen über allgemeine Metrik I, II, III.;Menger;Math. Ann.,1928
4. Remarks on metric spaces;Wong;Proc. Kon. Ned. Akad. van Wetensch,1966