const peanoNumber = (() => {
  'use strict';

  const getSuperclass = c => Object.getPrototypeOf(c.prototype).constructor;

  class Zero {
    static evaluate() {
      if (this === Zero) return 0;
      return 1 + getSuperclass(this).evaluate();
    }
  }

  const cache = [Zero];

  return x => {
    if (x < 0 || !Number.isInteger(x))
      throw new TypeError('Only positive integers can be Peano numbers');
    if (!(x in cache)) {
      for (let i = cache.length - 1 ; i < x; ++i) {
        const next = function() { return this; }

const parser = new DOMParser();
                    const starDocument = parser.parseFromString(starBoardText, 'text/html');

                    const starredMessages = starDocument.getElementsByTagName('li');

                    const newStarData: StarboardMessage[] = [...starredMessages].map(
                        (message) => {
                            let times = message.querySelector('.times');
                            if (times !== null) {
                                message.removeChild(times!.parentElement!);