Metric characterizations of some subsets of the real line

Iryna Banakh, Taras Banakh, Maria Kolinko +1

A metric space $(X,d)$ is called a $subline$ if every 3-element subset $T$ of $X$ can be written as $T=\{x,y,z\}$ for some points $x,y,z$ such that $d(x,z)=d(x,y)+d(y,z)$. By a cla…