The program has "in mind" a word (love) and you have to guess this word: letter by letter.
		Unless you don't guess the first letter the program does not ask for the next letter.
		If you guess a letter the program says: OK. And asks for the next one.
		?- start.
		Guess first letter|: m.
		false.
		?- start.
		Guess first letter|: l.
		OK.  Next letter|: a.
		Fail. Try again! Next letter|: o.
		OK.  Next letter|: v.
		OK.  Next letter|: e.
		OK. Congratulations! The word is [l,o,v,e]
		true.

		in_mind([l,o,v,e]).

		start:- write('Guess first letter'),read(X),
			in_mind([X|T]),write('OK. '),guess(T).

		guess([]):- write('Congratulations! The word is '),in_mind(W),write(W),!.
		guess(L):-  repeat,write('Next letter'),read(X),
	                    ((L=[X|T1],write('OK. '),guess(T1));
		             (write('Fail. Try again!'),guess(L))).