% glogic01.pl --- logic programming model for extensive form games.
% created: 22 Aug 2003. (was: glogic.pl, 10 July 2003).
% modified: 14,17 Sep 2003.
% References:
% Bonanno-Vilks's propositional logic modeling for game tree.
% Aumann(1995, GEB)'s theorem of the backward induction under common knowledge.


% extensive form game theory : game tree model
%------------------------------------------

terminal([c,a]).
terminal([d,a]).
%terminal([b]).
terminal([e,b]).
terminal([f,b]).

% payoff (play_history,player,payoff).
payoff([c,a],1,0).
payoff([d,a],1,2).
%payoff([b],1,1).
payoff([e,b],1,4).
payoff([f,b],1,1).

payoff([c,a],2,3).
payoff([d,a],2,2).
%payoff([b],2,0).
payoff([e,b],2,3).
payoff([f,b],2,4).

player(1).
player(2).


% player's information (player,name,path)
players_information(1,h1,[]).
players_information(2,h2,[a]).
players_information(2,h3,[b]).

node(terminal,Y):-
   terminal(Y).

node(players_information(J,H),Y):-
   players_information(J,H,Y).

% possible act at information set(name,player,act) 
possible_act(h1,1,a).
possible_act(h1,1,b).
possible_act(h2,2,c).
possible_act(h2,2,d).
possible_act(h3,2,e).
possible_act(h3,2,f).



% a game play simulator --- not always rational one
%----------------------------------------------

generate_play_history([],[]).
generate_play_history([J|P],[A|Y]):-
   length(Y,K),
   (K>1->!,fail;true),
   generate_play_history(P,Y),
   players_information(J,H,Y),
   possible_act(H,J,A).

% rational play model  ---- backward induction
% for perfect information games.
%----------------------------------------------

is_rational_play(J,A,H,Y):-
   players_information(J,H,Y),
   max(U,inductive_payoff([A|Y],J,U)).

inductive_payoff(Y,J,U):-
   payoff(Y,J,U).

inductive_payoff(Y,J,U):-
   % member((H,Y),[(h1,[a]),(h2,[b]),(h3,[])]),
   is_rational_play(_J1,A,_H,Y),
   inductive_payoff([A|Y],J,U).

inductive_payoff_vector(Y,Js,Us):-
   node(_,Y),
   findall(J,player(J),Js),   
   findall(U,
     (
      player(J),
      inductive_payoff(Y,J,U)
     ),
   Us).   


% maximal solution for given goal clause : a naive solver 
%---------------------------------------------------------

max(X,Goal):-
  % X: the objective variable,
  % Goal: the objective function and constraints,
  setof((X,Goal),Goal,Z),
  member((X,Goal),Z),
  \+ (
    member((Y,_),Z),
    Y > X
  ).





/* game tree in fig.12.2 of Vilks(1997) */

%    [0]
%     |   a1
%     |_____[1]
%     |      |    c2
%     |      |______[3]
%     |      |    d2
%     |      |______[4]
%     |   b1
%     |_____[2]

example(1,[
 (a1;b1),
 \+ (a1,b1),
 (a1->(c2;d2)),
 ((c2;d2)->a1),
 \+ (c2,d2),
 (b1->(pai(1)=1,pai(2)=0)),
 (c2->(pai(1)=1,pai(2)=0)),
 (d2->(pai(1)=0,pai(2)=1))
]).


%    [0]
%     |   a1
%     |_____[1]
%     |      |    c2
%     |      |______[3]
%     |      |    d2
%     |      |______[4]
%     |   b1
%     |_____[5]
%            |    e2
%            |______[6]
%            |    f2
%            |______[7]


example(2,[
 (a1;b1),
 \+ (a1,b1),
 (a1->(c2;d2)),
 ((c2;d2)->a1),
 \+ (c2,d2),
 (b1->(e2;f2)),
 \+ (e2,f2),
 (c2->(pai(1)=0,pai(2)=4)),
 (d2->(pai(1)=2,pai(2)=3)),
 (e2->(pai(1)=3,pai(2)=2)),
 (f2->(pai(1)=4,pai(2)=1))
]).

% 
rationality(2,[
 (c2;d2;e2;f2),
 (e2->(pai(2)=<2)),
 (c2->(pai(2)>=4)),
 2<4
],
'|-->',
 [\+ e2]
).




% end of program