Geodesic
Steiner mapping of three points on Euclidean plane
Vestnik Moskovskogo universiteta. Matematika, mehanika, no. 1 (2018), pp. 20-26 
K. V. Chesnokova. Steiner mapping of three points on Euclidean plane. Vestnik Moskovskogo universiteta. Matematika, mehanika, no. 1 (2018), pp. 20-26. http://geodesic.mathdoc.fr/item/VMUMM_2018_1_a2/
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     title = {Steiner mapping of three points on {Euclidean} plane},
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     year = {2018},
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     url = {http://geodesic.mathdoc.fr/item/VMUMM_2018_1_a2/}
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Voir la notice de l'article provenant de la source Math-Net.Ru

For Euclidean plane $\mathbb{C}$ we consider the Steiner mapping associating any three points $a, b, c$ with their median $s$ and the corresponding operator $P_D$ of metric projection of the space $l_1^3(\mathbb{C})$ onto its diagonal subspace $D=\{(x, x, x) \colon x \in \mathbb{C}\}$, $P_D(a, b, c)=(s, s, s) \colon s$. The exact value of the linearity coefficient of $P_D$ is calculated.

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