data/advent07-small.txt

   1 Step C must be finished before step A can begin.
   2 Step C must be finished before step F can begin.
   3 Step A must be finished before step B can begin.
   4 Step A must be finished before step D can begin.
   5 Step B must be finished before step E can begin.
   6 Step D must be finished before step E can begin.
   7 Step F must be finished before step E can begin.