generators.ET0LTreeGrammar:
( { edge, edge2, corner, corner2  },
  { inner:0, edge:0, edge2:0, corner:0, corner2:0, q:4, d:4, h:2 },
  {
    {
      corner -> corner2,
      edge -> edge2,
      corner2 -> d[inner, edge, edge, corner],
      edge2 -> h[inner, edge]
    }
  },
  q[corner, corner, corner, corner] )
