:- table win/1, p/0, q/0, r/0.

win(X) :- move(X,Y), tnot(win(Y)).

move(a,b).
move(b,a).
move(b,c).
move(c,d).

p :- tnot(q).
q :- tnot(p).
r :- p.
r :- q.