generators.ET0LTreeGrammar:
(
  { A, F },
  { F:0, conc:5, conc:2, enc+:1, enc+:2, enc-:1, enc-:2,
    enc:1, -:1, empty:0 },
  {
    {
      A -> conc[enc[A],F,enc+[A,enc+[A]],enc-[A],enc-[F,-[A]]],
      F -> conc[F,F]
    },
    {
      A -> empty,
      F -> F
    }
  },
  A, 1+ 2
)
