2 problems

Let $G(n,k)$ be a non-bipartite generalized Petersen graph, and let $f$ be an endomorphism of $G(n,k)$. The retract-image conjecture. The image of $f$ is a retract of $G(n,k)$. The…

Retraction characterization of hyper-median partial cubes. A partial cube is hyper-median if and only if it is a retract of a Cartesian product of bipartite cellular graphs.