% IR

%rule

:-unknown(P,fail).
%15(1)
become_effective(offer(A,B,C),T1):-
    	reach(offer(A,B,C),B,T1),
        \+(become_effective(withdrawl(A,B,offer(A,B,C)),T2)).
%15(2)
become_effective(withdrawl(A,B,offer(A,B,C)),T2):-
        reach(withdrawl(A,B,offer(A,B,C)),B,T2),
        \+((reach(offer(A,B,C),B,T1),before(T1,T2))).

%16(1)
become_effective(revocation(A,B,offer(A,B,C),T):-
        reach(revocation(A,B,C),B,T),
        \+(((dispatched_an_acceptance,T1),before_or_at_the_same_time(T1,T))).




\+(become_effective(offer(A,B,C),T1)):-
        reach(revocoation(A,B,offer(A,B,C),B,T1)

%%HY このように否定号をヘッドに持つようなルールはPrologでは赦されません。取消効力発生を何かの傷害要件として形式化してはどうでしょうか。


%18(2)
become_effective(acceptance(B,A,D),T):-
    reach(acceptance(B,A,D),A,T),
        become_effective(offer(A,B,C),T1).

%23
is_concluded(contract(A,B,C),T):-
    become_effective(acceptance(B,A,offer(A,B,C)),T).
        
before(T1,T2):-
    T1@<T2.

%fact(3d)

reach(offer(anzai,bernard,sale(agriculture_machine,'$50000')),bernard,t0408).
reach(acceptance(bernard,anzai,offer(anzai,bernard,sale(agriculture_machine, '$50000'))),anzai,t0410).
reach(withdrawl(anzai,bernard,offer(anzai,bernard,sale(agriculture_machine, '$50000'))),bernard,t0409).