generators.ET0LTreeGrammar("without delay"):
(
  { S, T },
  { sp:3, 2sp:3, square:0 },
  {
    {
      S -> 2sp[S, T, T],
      T -> sp[S, S, T]
    },
    {
      S -> square,
      T -> square
    }
  },
  S
)
