Topological Sort

A topological sort of a Directed Acyclic Graph $G=(V,E)$ is an ordered list of vertices $L=⟨v_1,v_2,\dots ,v_n⟩$, such that:

$$\text{if }{v}_i⇝v_j\text{ then }i<j\text{for all }i,j\le n$$

All the arrows point ‘downstream’ from $v_1$ to $v_n$.