function elements(args) {
  assert(args.length !== 0, "elements: at least one parameter expected");

  return arbitraryBless({
    generator: generator.bless(function (/* size */) {
      var i = random(0, args.length - 1);
      return args[i];
    }),

    shrink: shrink.bless(function (x) {
      var idx = args.indexOf(x);
      if (idx <= 0) {
        return [];
      } else {
        return args.slice(0, idx);
      }
    }),
    show: show.def,
  });
}
- `elements(args: array a): arbitrary a`

      Random element of `args` array.