/************************************************
 File: empty0.pl
 Author: Mihaela Malita
 Title:  The emptiness problem. L(G) = 0 ?
 Find if your grammar generates at least one word.
 Example.
         ?- start.
        Check if our grammar generates any word
        generated-[a, b]
        
        Yes
***************************************************/ 
start:- write('Check if our grammar generates any word\n'),
        empty_grammar.
        
/*        L(G)= a^nb^n. Grammar is

  s --> [a],[b].  s --> [a],s,[b].

*/      

/*  Same in grammar but in Chomsky normal form.
*/
  s --> xa,xb.
  xa --> [a].
  xb --> [b].
  s --> xa,y.
  y --> s,xb.
  
% check if there is any word generated by the grammar
% prints first word then stops
    
    empty_grammar:- phrase(s,W),
                    write(generated-W).