Directed path:   list of n ≥ 2 vertices v₁, v₂, ... v_n

• where (v_i,v_i+1) ∈ edges(G) for all (v_i,v_i+1) in list
• if v₁ = v_n, we have a directed cycle

Indegree of vertex: d^-1(v) = number of edges like (_, v)

Reachability:   w is reachable from v if ∃ directed path v,...,w

Strong connectivity:   every vertex is reachable from every other vertex

Directed acyclic graph (DAG):   graph containing no directed cycles