1 % The meaning of the time predicate is self-evident. As for the disk
   2 % predicate, there are k disks 1,2,...,k. Disks 1, 2, 3, 4 denote pegs. 
   3 % Disks 5, ... are "movable". The larger the number of the disk, 
   4 % the "smaller" it is.
   5 %
   6 % The program uses additional predicates:
   7 % on(T,N,M), which is true iff at time T, disk M is on disk N
   8 % move(t,N), which is true iff at time T, it is disk N that will be
   9 % moved
  10 % where(T,N), which is true iff at time T, the disk to be moved is moved
  11 % on top of the disk N.
  12 % goal, which is true iff the goal state is reached at time t
  13 % steps(T), which is the number of time steps T, required to reach the goal (provided part of Input data)
  14 
  15 % Read in data 
  16  	on(0,N1,N) :- on0(N,N1).
  17     onG(K,N1,N) :- ongoal(N,N1), steps(K).
  18 		   
  19 % Specify valid arrangements of disks
  20  	% Basic condition. Smaller disks are on larger ones
  21  	:- time(T), on(T,N1,N), N1>=N.
  22  	
  23 % Specify a valid move (only for T<t)
  24  	% pick a disk to move
  25     move(T,N) | noMove(T,N) :- disk(N), time(T), steps(K), T<K.
  26     :- move(T,N1), move(T,N2), N1 != N2.
  27     :- time(T), steps(K), T<K, not diskMoved(T).
  28     diskMoved(T) :- move(T,Fv1).
  29 
  30  	% pick a disk onto which to move
  31     where(T,N) | noWhere(T,N) :- disk(N), time(T), steps(K), T<K.
  32     :- where(T,N1), where(T,N2), N1 != N2.
  33     :- time(T), steps(K), T<K, not diskWhere(T).
  34     diskWhere(T) :- where(T,Fv1).
  35 
  36  	% pegs cannot be moved
  37  	:- move(T,N), N<5.
  38 
  39  	% only top disk can be moved
  40  	:- on(T,N,N1), move(T,N).
  41 
  42  	% a disk can be placed on top only.
  43  	:- on(T,N,N1), where(T,N).
  44 
  45  	% no disk is moved in two consecutive moves
  46  	:- move(T,N), move(TM1,N), TM1=T-1.
  47 
  48 % Specify effects of a move
  49  	on(TP1,N1,N) :- move(T,N), where(T,N1), TP1=T+1.
  50 
  51  	on(TP1,N,N1) :- time(T), steps(K), T<K,
  52  	                on(T,N,N1), not move(T,N1), TP1=T+1.
  53 
  54 % Goal description
  55 	 :- not on(K,N,N1), onG(K,N,N1), steps(K).
  56 	 :- on(K,N,N1), not onG(K,N,N1),steps(K).
  57 
  58 % Solution
  59 	 put(T,M,N) :- move(T,N), where(T,M), steps(K), T<K.