coveredEntries = (sorted, [leftIndex, rightIndex]) => {
  /** @type {Iterable<[number, Passable]>} */
  const iterable = harden({
    [Symbol.iterator]: () => {
      let i = leftIndex;
      return harden({
        next: () => {
          if (i <= rightIndex) {
            const element = sorted[i];
            i += 1;
            return harden({ value: [i, element], done: false });
          } else {
            return harden({ value: undefined, done: true });
          }
        },
      });
    },
  });
  return iterable;
}
@param {Passable[]} sorted
@param {IndexCover} indexCover
@returns {Iterable<[number, Passable]>}