%% 法学部法律学科???????? SM
%%HY 解答ファイルの先頭に??????と???を最初に記入して下さい。
%%HY コンサルトのところのtraceは不必要です。
%%HY 下記は正解です。

SICStus 3.12.7 (x86-win32-nt-4): Fri Oct  6 00:15:14 WEST 2006
Licensed to mita.cc.keio.ac.jp
| ?- ['contract(3b).txt'].
% consulting h:/contract(3b).txt...
* [T2] - singleton variables in user:become_effective/2
* Approximate lines: 4-8, file: 'h:/contract(3b).txt'
* [C,T2] - singleton variables in user:become_effective/2
* Approximate lines: 8-12, file: 'h:/contract(3b).txt'
% consulted h:/contract(3b).txt in module user, 0 msec 1840 bytes
yes
| ?- trace.
% The debugger will first creep -- showing everything (trace)
yes
% trace
| ?-
| ?- ['contract(3b).txt'].
% consulting h:/contract(3b).txt...
* [T2] - singleton variables in user:become_effective/2
* Approximate lines: 4-8, file: 'h:/contract(3b).txt'
* [C,T2] - singleton variables in user:become_effective/2
* Approximate lines: 8-12, file: 'h:/contract(3b).txt'
% consulted h:/contract(3b).txt in module user, 0 msec -56 bytes
yes
% trace
| ?-
| ?- is_concluded(X,T).
        1      1 Call: is_concluded(_463,_483) ?
        2      2 Call: become_effective(acceptance(_1106,_1105,offer(_1105,_1106
,_1107)),_483) ?
        3      3 Call: reach(acceptance(_1106,_1105,offer(_1105,_1106,_1107)),_1
105,_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) ?
        1      1 Exit: is_concluded(contract(anzai,bernard,sale(agriculture_mach
ine,'$50000')),t0409) ?
T = t0409,
X = contract(anzai,bernard,sale(agriculture_machine,'$50000')) ?
yes
% trace
| ?-