Define Nested Table Type

CREATE OR REPLACE TYPE strings_nt IS TABLE OF VARCHAR2 (100) 

Exercise SUBMULTISET

DECLARE  
   steven_authors   strings_nt  
                       := strings_nt ('ROBIN HOBB',  
                                      'ROBERT HARRIS',  
                                      'DAVID BRIN',  
                                      'SHERI S. TEPPER',  
                                      'CHRISTOPHER ALEXANDER');  
  
   eli_authors      strings_nt  
      := strings_nt ('SHERI S. TEPPER', 'DAVID BRIN');  
  
   null_authors      strings_nt  
      := strings_nt ();  
  
   PROCEDURE bpl (val IN BOOLEAN, text_in IN VARCHAR2)  
   IS  
   BEGIN  
      DBMS_OUTPUT.put_line (text_in || ' ' ||  
         CASE val  
            WHEN TRUE THEN 'TRUE'  
            WHEN FALSE THEN 'FALSE'  
            ELSE 'NULL'  
         END);  
   END bpl;  
BEGIN  
   bpl (steven_authors SUBMULTISET OF eli_authors,  
        'Father follows son?');  
  
   bpl (eli_authors SUBMULTISET OF steven_authors,  
        'Son follows father?');  
  
   bpl (steven_authors NOT SUBMULTISET OF eli_authors,  
        'Father doesn''t follow son?');  
  
   bpl (eli_authors NOT SUBMULTISET OF steven_authors,  
        'Son doesn''t follow father?');  
  
   bpl (steven_authors SUBMULTISET OF null_authors,  
        'Steven in NULL?');  
END;