Towers of Hanoi
---------------

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.


Quicksort
---------

split(H,[A|X],[A|Y],Z) :- A =< H, split(H,X,Y,Z).
split(H,[A|X],Y,[A|Z]) :- A > H, split(H,X,Y,Z).
split(_,[],[],[]).

qsort([],[]).
qsort([H|T],S) :- 
  split(H,T,A,B),
  qsort(A,A1),
  qsort(B,B1),
  append(A1,[H|B1],S).

append([],L,L).
append([H|T],L,[H|V]) :- append(T,L,V).