generators.ET0LTreeGrammar:
( { S0, S, A, B },
  { F:4, G:4, sq:0, -:0 },
  {
    {
      S0 -> F[S,S,S,-],
      S -> F[S,S,S,S]
    },
    {
      S -> F[A,B,B,A],
      A -> G[G[-,-,-,sq],
             G[-,-,sq,sq],
	     G[-,sq,-,sq],
	     G[sq,sq,sq,-]],
      B -> G[G[-,-,-,sq],
             G[-,-,sq,-],
             G[-,sq,-,sq],
	     G[sq,-,sq,-]]
    }
  },
  S0,
  1+ 2 2
)
