text: #ifndef __HEADER_1_H__
  #define __HEADER_1_H__
  
  #include <iostream>
  #include <stdio.h>
  #include "a.h"
  using namespace std;
  
  void mega_test(){
      cout<<"Calling library a.h from b.h: "<<endl;
      test();
  }
  
  
  #endif;