no. 4
The convexity of the subset space of a metric space
Compositio Mathematica, Tome 22 (1970) no. 4, pp. 383-385 
@article{CM_1970__22_4_383_0,
     author = {Bryant, V. W.},
     title = {The convexity of the subset space of a metric space},
     journal = {Compositio Mathematica},
     pages = {383--385},
     year = {1970},
     publisher = {Wolters-Noordhoff Publishing},
     volume = {22},
     number = {4},
     mrnumber = {275293},
     zbl = {0205.27102},
     language = {en},
     url = {https://www.numdam.org/item/CM_1970__22_4_383_0/}
}
TY  - JOUR
AU  - Bryant, V. W.
TI  - The convexity of the subset space of a metric space
JO  - Compositio Mathematica
PY  - 1970
SP  - 383
EP  - 385
VL  - 22
IS  - 4
PB  - Wolters-Noordhoff Publishing
UR  - https://www.numdam.org/item/CM_1970__22_4_383_0/
LA  - en
ID  - CM_1970__22_4_383_0
ER  - 
%0 Journal Article
%A Bryant, V. W.
%T The convexity of the subset space of a metric space
%J Compositio Mathematica
%D 1970
%P 383-385
%V 22
%N 4
%I Wolters-Noordhoff Publishing
%U https://www.numdam.org/item/CM_1970__22_4_383_0/
%G en
%F CM_1970__22_4_383_0
Bryant, V. W. The convexity of the subset space of a metric space. Compositio Mathematica, Tome 22 (1970) no. 4, pp. 383-385. https://www.numdam.org/item/CM_1970__22_4_383_0/

L.M. Blumenthal [1] Distance Geometry, Oxford, 1953. | Zbl | MR

C. Kuratowski [2] Topologie I (2nd edition), Warsaw, 1948. | Zbl

C. Kuratowski [3] Topologie II, Warsaw, 1950. | Zbl