digraph CFG_examples {
  node [shape=circle width=0.3 height=0.3 label="" fixedsize=true]
  edge [arrowsize=0.5]
  if -> { then; else } -> fi
  while -> body [weight=3]
  body -> while:w
  while -> end
  body -> end [style="invis" weight=3]
  fi -> exit1 [style="invis"]
  exit1 -> exit2
  exit2 -> body2 [weight=4]
  body2 -> exit1:w
  exit1 -> out:e
  exit2 -> out
  body2 -> out [style="invis" weight=4]
  end -> top [style="invis"]
  top -> entry1 [weight=2]
  entry1 -> out2
  top -> entry2:w 
  entry1 -> entry2 [weight=4]
  entry2 -> entry1:w
  entry2 -> out2 [style="invis" weight=4]
  if [xlabel = "(a)"]
  while [xlabel = "(b)"]
  exit1 [xlabel = "(c)"]
  top [xlabel = "(d)"]
} /*end digraph*/