text: #pragma once
  
  #include <iostream>
  #include <vector>
  
  void sort_article_files(std::istream& article_titles_file, std::istream& article_dates_file, std::ostream& article_titles_output_file, std::ostream& article_dates_output_file);
  void sort_category_files(std::istream& category_titles_file, std::ostream& category_titles_output_file);
  