generators.BSTGrammar: extended translation
  ( { C, E },
    { quarters:4, corner:4, edge:2, a-part:0, b-part:0, empty:0 },
    { 1, 2 },
    2,
    {
      {
        {
          C -> corner[a-part, E<1 2>,C<1 1>,E<1 2>],
          E -> edge[a-part, E<1 1>]
        },
        {
          C -> corner[b-part, E<1 2>,C<1 1>,E<1 2>],
          E -> edge[b-part, E<1 1>]
        }
      },
      {
        {
          C -> empty, E -> empty
        }
      } weight 0
    },
    quarters[C<1 1>,C<1 1>,C<1 1>,C<1 1>] )
