let

  closure = builtins.genericClosure {
    startSet = [ { key = 80; } ];
    operator =
      {
        key,
        foo ? false,
      }:
      if builtins.lessThan key 0 then
        [ ]
      else
        [
          { key = builtins.sub key 9; }
          {
            key = builtins.sub key 13;
            foo = true;
          }
        ];
  };

  sort = (import ./lib.nix).sortBy (a: b: builtins.lessThan a.key b.key);

in
sort closure