  end {
    @m = {
      "a": {
        "x": [1,2,3],
        "y": [4,5,6],
      },
      "b": {
        "s": [7,8,9],
        "t": [9,5,1],
      },
    };
    unset @m["a"][[1]];
    emit @m;
  }
