sequence::sequence(const sequence& source)
{
if (source.cursor == NULL)
          {
               list_copy(source.head_ptr, head_ptr, tail_ptr);
               cursor = NULL;
               precursor = NULL;
          }
     //the next two branch statements are the problem
else if (source.cursor==source.head_ptr)
               {
                    list_copy(source.head_ptr, head_ptr, tail_ptr);//copy the list
                    cursor = head_ptr; //set cursor to the  first node in the list
                    precursor = NULL;//set the precursor to null
               }
else
                     {
                         //divide the target list into two peices one starting at the head and ending at the precursor
                         //the other starting with the cursor and ending at the tail node
                          list_piece(source.head_ptr, source.cursor, head_ptr, precursor);
                          list_piece(source.cursor, NULL, cursor, tail_ptr);
                          //set  the precursor's link to the cursor
                          precursor->set_link(cursor);
                     }
 ////////////////////////////////////
       many_nodes = source.many_nodes;
      return;

   }

void sequence::operator =(const sequence& source){
    //check if the  source sequence is the desitnation sequence
      if (this == &source)
      {
           return;
      }
      //if the list is empty
          if (source.many_nodes==0)
          {
               list_copy(source.head_ptr, head_ptr, tail_ptr);//copy the source list into the destination list
               cursor = NULL;//set cursor to null
               precursor = NULL;//set the precursor to null
          }
               //The next two branch statements is where the problem is
          else if (source.cursor==source.head_ptr)//if the list only has one element
               {
                    list_copy(source.head_ptr, head_ptr, tail_ptr);//copy the source list into the destination list
                    cursor = head_ptr;//set cursor to first element in list
                    precursor = NULL;//set precursor to null
               }
          else//if the sequence has more than one element
                     {
                         //divide the target list into two peices one starting at the head and ending at the precursor
                         //the other starting with the cursor and ending at the tail node
                          list_piece(source.head_ptr, source.cursor, head_ptr, precursor);//
                          list_piece(source.cursor, NULL, cursor, tail_ptr);
                          //link the two peices together
                          precursor->set_link(cursor);
                     }
          //////////////////////////////////////
      many_nodes = source.many_nodes;
      return 0;