Distance labelings: a generalization of Langford sequences

A Langford sequence of order $m$ and defect $d$ can be identified with a labeling of the vertices of a path of order $2m$ in which each labeled from $d$ up to $d+m-1$ appears twice and in which the vertices that have been label with $k$ are at distance $k$. In this paper, we introduce two generalizations of this labeling that are related to distances.