ld2 is ld1 (the load after the store is the same node): True
a load through AFTER(p, store) is a different node: True
  sequenced program, order=id: buf = [20.0]  (1 -> store 2 -> load 2 -> store 20)
  sequenced program, order=dfs: buf = [20.0]  (1 -> store 2 -> load 2 -> store 20)
  unsequenced program, order=id: buf = [5.0, 5.0, 0.0]
  unsequenced program, order=dfs: buf = [5.0, 1.0, 0.0]
  the two orders disagree: with no AFTER edge the program has no single meaning
