text: #ifndef RUNGE_KUTTA_4TH_INIT_VAL_PROBLEM_H
  #define RUNGE_KUTTA_4TH_INIT_VAL_PROBLEM_H
  
  #include "type.h"
  
  points* euler(initval_problem*, points*);
  points* fixed_euler(initval_problem*, points*);
  points* runge_kutta_4th(initval_problem*, points*);
  
  #endif
  