Geodesic
ACCRETIVE METRIC PROJECTIONS
Acta mathematica Universitatis Comenianae, Tome 60 (1991) no. 1 
L. Vesely. ACCRETIVE METRIC PROJECTIONS. Acta mathematica Universitatis Comenianae, Tome 60 (1991) no. 1. http://geodesic.mathdoc.fr/item/AMUC_1991_60_1_a3/
@article{AMUC_1991_60_1_a3,
     author = {L. Vesely},
     title = {ACCRETIVE {METRIC} {PROJECTIONS}},
     journal = {Acta mathematica Universitatis Comenianae},
     year = {1991},
     volume = {60},
     number = {1},
     url = {http://geodesic.mathdoc.fr/item/AMUC_1991_60_1_a3/}
}
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Voir la notice de l'article provenant de la source Comenius University

In this note we prove that all metric projections onto closed subsets of a normed linear space $X$ are \a e if and only if $X$ is an inner-product space. Instead of all closed sets it suffices to consider more special classes of sets in $X$.