%TS

| ?- listing.
become_effective(withdrawl(A,B,offer(A,B,C),D)) :-
        reach(withdrawl(A,B,C), B, D),
        \+ (reach(offer(A,B,C),B,E),E@<D).

become_effective(offer(A,B,C), D) :-
        reach(offer(A,B,C), B, D),
        \+become_effective(withdrawl(A,B,offer(A,B,C)),_).
become_effective(withdrawl(A,B,offer(A,B,C)), D) :-
        reach(withdrawl(A,B,offer(A,B,C)), B, D),
        \+ (reach(offer(A,B,C),B,E),E@<D).
become_effective(acceptance(A,B,C), D) :-
        reach(acceptance(A,B,C), B, D).

is_concluded(contract(A,B,C), D) :-
        become_effective(acceptance(B,A,offer(A,B,C)), D),
        become_effective(offer(A,B,C), _).

reach(withdrawl(anzai,bernard,offer(anzai,bernard,sale(agriculture_machine,'$500
00'))), bernard, t0407).
reach(offer(anzai,bernard,sale(agriculture_machine,'$50000')), bernard, t0408).
reach(acceptance(bernard,anzai,offer(anzai,bernard,sale(agriculture_machine,'$50
000'))), anzai, t0409).

yes
% trace

| ?- is_concluded(X,Y).
        1      1 Call: is_concluded(_463,_483) ?
        2      2 Call: become_effective(acceptance(_1116,_1115,offer(_1115,_1116
,_1117)),_483) ?
        3      3 Call: reach(acceptance(_1116,_1115,offer(_1115,_1116,_1117)),_1
115,_483) ?
        3      3 Exit: reach(acceptance(bernard,anzai,offer(anzai,bernard,sale(a
griculture_machine,'$50000'))),anzai,t0409) ?
        2      2 Exit: become_effective(acceptance(bernard,anzai,offer(anzai,ber
nard,sale(agriculture_machine,'$50000'))),t0409) ?
        4      2 Call: become_effective(offer(anzai,bernard,sale(agriculture_mac
hine,'$50000')),_1099) ?
        5      3 Call: reach(offer(anzai,bernard,sale(agriculture_machine,'$5000
0')),bernard,_1099) ?
        5      3 Exit: reach(offer(anzai,bernard,sale(agriculture_machine,'$5000
0')),bernard,t0408) ?
        6      3 Call: become_effective(withdrawl(anzai,bernard,offer(anzai,bern
ard,sale(agriculture_machine,'$50000'))),_4398) ?
        7      4 Call: reach(withdrawl(anzai,bernard,offer(anzai,bernard,sale(ag
riculture_machine,'$50000'))),bernard,_4398) ?
        7      4 Exit: reach(withdrawl(anzai,bernard,offer(anzai,bernard,sale(ag
riculture_machine,'$50000'))),bernard,t0407) ?
        8      4 Call: reach(offer(anzai,bernard,sale(agriculture_machine,'$5000
0')),bernard,_6460) ?
        8      4 Exit: reach(offer(anzai,bernard,sale(agriculture_machine,'$5000
0')),bernard,t0408) ?
        9      4 Call: t0408@<t0407 ?
        9      4 Fail: t0408@<t0407 ?
        6      3 Exit: become_effective(withdrawl(anzai,bernard,offer(anzai,bern
ard,sale(agriculture_machine,'$50000'))),t0407) ?
        4      2 Fail: become_effective(offer(anzai,bernard,sale(agriculture_mac
hine,'$50000')),_1099) ?
        1      1 Fail: is_concluded(_463,_483) ?
no
% trace
| ?-

/* %%HY
課題提出有り難うございました。
これで事例3cは正しい解が出るようになりましたね。
同じruleで3dを解いてみて下さい。
そしてそのログとともに答えが正しいかどうか返事下さい。
更に３ｄが解けるように改訂して下さい。
*/