text: #ifndef _List_H
  
  #define _List_H
  
  struct Node;
  typedef struct Node *PtrToNode;
  typedef PtrToNode List;
  typedef PtrToNode Position;
  typedef int ElementType;
  
  // List MakeEmpty(List L);
  // int IsEmpty(List L);
  // int IsLast(Position P, List L);
  // void Delete(ElementType X, List L);
  // Position FindPrevious(ElementType X, List L);
  // void Insert(ElementType X, List L, Position P);
  // void DeleteList(List L);
  // Position Header(List L);
  // Position First(List L);
  // Position Advance(Position P);
  // ElementType Retrieve(Position P);
  
  #endif
  
  /* Place in the implementation file */
  struct Node
  {
      ElementType Element;
      Position Next;
  };