/* The Towers of Hanoi problem: */

/* 3 pegs, n discs */
/* n discs are stacked in order, bigggest at bottom, smallest at top */
/* all on one peg ... move the n discs to one of the other 2 pegs */
/* moving only one disc at a time and never resting a larger disc on */
/* a smaller one.  The aim is to solve the 64-disc problem */

xfer(0,_,_,_).

xfer(N,Init,Dest,Temp) :- 
   N>0, N1 is N-1,
   xfer(N1,Init,Temp,Dest),
   write('Move disc '), write(N),
   write(' from '),     write(Init),
   write(' to '),       write(Dest),   nl,
   xfer(N1,Temp,Dest,Init).


/* Solution to the 64 discs problem is given by... */
/* ?- xfer(64,a,b,c). */

/* but DONT run this: it takes quite a while to complete!! */
/* instead try ?- xfer(3,left,middle,right) */
/* try ?- xfer(4,left,middle,right) */
/* try ?- xfer(5,left,middle,right) */
/* try even ?- xfer(9,left,middle,right) */