text: let numUniqueEmails = emails => {
      const email_set = new Set;
      for (let email of emails){
          let [local, domain] = _.split(email, "@");
          local = _.split(local, '+', 1)[0];
          email_set.add([_.split(local, '.').join(""), domain].join("@"));
      }
      return email_set.size
  };
  