#include <incmode>.

#program base.
peg(a;b;c).
disk(1..7).
init_on(1..7,a).
goal_on(1..7,b).

on(D,P,0) :- init_on(D,P).

#program step(t).
1 { move(D,P,t) : disk(D), peg(P) } 1.

move(D,t)        :- move(D,P,t).
on(D,P,t)        :- move(D,P,t).
on(D,P,t)        :- on(D,P,t-1), not move(D,t).
blocked(D-1,P,t) :- on(D,P,t-1).
blocked(D-1,P,t) :- blocked(D,P,t), disk(D).

:- move(D,P,t), blocked(D-1,P,t).
:- move(D,t), on(D,P,t-1), blocked(D,P,t).
:- not 1 { on(D,P,t) } 1, disk(D).

#program check(t).
:- query(t), goal_on(D,P), not on(D,P,t).

#show move/3.