%%% Better world problem
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% There are M (max_people) people X in {1,2,...,M}
%%% Each of them at the beginning owns 2X Euros
%%% The goal is to obtain an equilibrium situation
%%% where the main difference between richness is 1
%%% Person X can donate to another person exactly
%%% X euros per action.
%%% No one can remain without money (at any state)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Invented and coded by DFP, 2007
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%% With this instance try :-sicsplan(4).

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max_people(5).
person(X) :- max_people(N), interval(X,1,N).

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fluent(owns(B),1,M):- person(B),
     max_people(N),M is N*(N+1).

%%%%%%%%%%%%%%%%

action(gives(X,Y)):-
       person(X),person(Y),neq(X,Y).

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executable(gives(X,Y),[owns(X) gt X ]) :-
        action(gives(X,Y)).

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causes(gives(X,Y), owns(X) eq owns(X)^(-1) - X, []):-
        action(gives(X,Y)).
causes(gives(X,Y), owns(Y) eq owns(Y)^(-1) + X, []) :-
        action(gives(X,Y)).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

:-dynamic(caused/2).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

initially(owns(X) eq  2*X) :-
    person(X).

%%%%%%%%%%%%%%%

goal(owns(X) leq owns(Y) + 1) :-
     person(X), person(Y), neq(X,Y).



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