generators.ET0LTreeGrammar("uncoloured hexagonal knots"):
( { A, B, T, N },
  { F:6, G: 4, H:3, I:2, tile1:0, tile2:0, tile3:0, outer:0, background:0, +:2, rot:1,
    A:0, B:0, T:0, N:0 },
  {
    {
      A -> G[N, rot[N], A, B],
      B -> H[T, rot[N], B],
      T -> tile1,
      N -> tile1
    },
    {
      A -> G[N, rot[N], A, B],
      B -> H[T, rot[N], B],
      T -> tile2,
      N -> tile2
    },
    {
      A -> G[N, N, A, B],
      B -> H[T, N, B],
      T -> tile3,
      N -> tile1
    },
    {
      A -> G[tile1, outer, background, background],
      B -> H[tile1, outer, background],
      T -> tile1,
      N -> tile1
    },
    {
      A -> G[tile2, outer, background, background],
      B -> H[tile2, outer, background],
      T -> tile2,
      N -> tile2
    },
    {
      A -> G[tile1, outer, background, background],
      B -> H[tile3, outer, background],
      T -> tile3,
      N -> tile1
    }
  },
  F[A, A, A, A, A, A],
  (1,2,3)* (4,5,6)
)
