/********************************************************
   File: dfa0.pl     System: SWI-Prolog  5.2.8
   Author: Mihaela Malita
   Date: 10/02/2003
   Title: Describe a DFA that accepts words that start with a.
   
   Alphabet={a,b}, States={0,1,2}   Favorable={1} start is state 0.
   Transition function is:
                delta(0,a)=1    delta(0,b)=2
                delta(1,a)=1    delta(1,b)=1
                delta(2,a)=2    delta(2,b)=2
 
   First load the file from folder C:/swimm 
   ?- ['C://swimm/dfa0.pl'].
   Yes
   List facts from your file (except comments).   
   ?- listing.
    favorable(1).
    
    start(0).
    
    delta(0, a, 1).
    delta(0, b, 2).
    delta(1, a, 1).
    delta(1, b, 1).
    delta(2, a, 2).
    delta(2, b, 2).
   What is the start state?
   ?- start(S).
    S=0
    Yes
   
   What is/are the favorable state(s)/
   ?- favorable(F).
    F=1
   
   How does delta/3 look like (your transition function)?
   ?- delta(X,Let,Y).
    X = 0
    Let = a
    Y = 1 ; % YOU type ; for more solutions
    
    X = 0
    Let = b
    Y = 2 ;
    
    X = 1
    Let = a
    Y = 1  % You type <ENTER> and it does not look for more
    Yes
    
   Is there any state that has a loop on itself?
   ?- delta(S,_,S).
    S = 1  % You type <ENTER>
    Yes
    
   Is the start state also favorable?
   ?- start(X),favorable(X).
    No
   
   For a certain state print all the arrows that go out.
   ?- delta(0,X,Q).
   ?- delta(0,X,Q).
    X = a
    Q = 1 ; % You type ;
    
    X = b
    Q = 2 ; % You type ; It is a request for MORE
    
    No    % it means "I" cannot find MORE
    
    For a certain state print all the states where you can go from it.
    ?- delta(0,_,X).
     X = 1 ; % You type ; asking for MORE
     X = 2 ;
     No
    
    Find the alphabet.
    ?- delta(_,X,_).
     X = a ;
     X = b ;
     No    
    ?- delta(0,X,Q),write([X,Q]),fail.
     [a, 1][b, 2]
     No
*************************************************/
/* This is the definition of your DFA in Prolog.
*/
    delta(0,a,1).
    delta(0,b,2).
    delta(1,a,1).
    delta(1,b,1).
    delta(2,a,2).
    delta(2,b,2).
    
    start(0).
    
    favorable(1).