Prologの技芸 12.3節の練習問題

(1)

% nim(N,S) :-
%  和がNで自分に回ってきたとき，Sと言えば勝てる．
nim(N,S) :- between(1,3,S), N1 is N+S, lose(N1), !.

:- dynamic win/1. 
:- dynamic lose/1. 
win(N) :-
 N =< 20, between(1,3,A),
 N1 is N+A, lemma(lose(N1)), !.
lose(20).
lose(N) :-
 N =< 20,
 N1 is N+1, N2 is N+2, N3 is N+3,
 lemma(win(N1)), lemma(win(N2)), lemma(win(N3)).