generators.ET0LTreeGrammar:
( { S, D },
  { F1:6, F2:9, F3:8, D:3, sq:0, -:0 },
  {
    {
      S -> F1[D,D,S,S,S,S],
      D -> D[D,D,D]
    },
    {
      S -> F2[D,S,D,D,S,D,D,S,D],
      D -> D[D,D,D]
    },
    {
      S -> F3[D,S,D,D,D,D,S,D],
      D -> D[D,D,D]
    },
    {
      S -> sq,
      D -> sq
    }
  },
  F1[D,D,S,S,S,S]
)
