graphs

Introduction An st-ordering (or bipolar odering) of a simple undirected graph is $G = (V, E)$ is a specific permutation $l$ of vertices, where any permutation $l$ induces a natural partial order on vertices $u < v \iff l(u) < l(v) \text{ and } uv \in E$. $l$ is called to be an st-ordering if and only if for a given pair of vertices $(s, t)$, $s$ (resp. $t$) is the unique minimal (resp....