# Tag Info

We can reduce it to the following problem: Given a directed graph on vertex set $\{1,2,\dots,n\}$, we want to know if there exists a permutation $T$ such that for each edge $(i,j)$ in the graph, $T[i]<T[j]$. The reduction: add an edge to the graph for each pair $i,j$ where both $P_b[i]$ and $P_b[j]$ exist for some $b \in \{0,1\}$; the orientation of ...