generators.regularTreeGrammar:
( { S, H, A },
  { a:0, b:0, c:1, h:2, v:2 },
  { S -> c[H],
    H -> h[H,H] weight 2,
    H -> c[A],
    A -> a,
    A -> b,
    A -> h[A,A] weight 2,
    A -> v[A,A] weight 2
  },
  S )
