hanoi(N) :- nl, nl, move(N,left,centre,right).
move(0,_,_,_) :- !.
move(N,A,B,C)
  :- M is N - 1,
     move(M,A,C,B),
     inform(A,B),
     move(M,C,B,A).
inform(X,Y) :- write('move disc from '),write(X),write(' pole to the '),
               write(Y),write(' pole.'),nl.