generators.ET0LTreeGrammar:
  (
    { I, C, A, B },
    { subst:2, line:0, refine:4, t:3, c:7, invert:1, X1:0, empty:0 },
    {
      {
        I -> invert[I],
        C -> c[C,C,C,C,C,C,C],
        A -> refine[B,B,B,B],
        B -> A % implement delay to slow down refinement of snowflake shape
      },
      {
        I -> X1,
        C -> t[X1,X1,X1],
        A -> line,
        B -> line
      }
    },
    subst[I,subst[C,A]]
  )
