const getRanksOverNumberOfBackLinks = (url) => {
          return getBackLinkedPages(url).map(backLinkPage => {
            return backLinkPage.rank / countOutLinks(backLinkPage.url)
          });
        };

        const normalizedSum = (ranksOverNumberOfBackLinks) => {
          return (1 - d) + d * sum(ranksOverNumberOfBackLinks);
        };

        const pageRank = normalizedSum(
          getRanksOverNumberOfBackLinks(
            url
          )
        );