generators.ET0LTreeGrammar:
(
  { A, B, F },
  { F:0, conc:3, conc:2, enc+:3, enc+:1, enc2-:2, 2-:1,
    empty:0 },
  {
    {
      A -> conc[enc+[F,enc+[A],2-[A]], enc2-[F, A], B],
      B -> conc[F,A],
      F -> conc[F,F]
    },
    {
      A -> empty,
      B -> empty,
      F -> F
    }
  },
  A, 1+ 2
)
