generators.ET0LTreeGrammar:
( { C, R, T },
  { diag:3, up:1, right:1, angle:0 },
  {
    {
      C -> diag[T, R, C],
      R -> right[R],
      T -> up[T]
    },
    {
      C -> angle,
      R -> angle,
      T -> angle
    }
  },
  C )
