% Program: Seat arrangement -- version 1 
% This version does not use the #domain definition 
% specify the number of person 
% to test this program run 
% lparse -c n=4 seat.lp | smodels 
% then run with 
% lparse -c n=3 seat.lp | smodels 

person(1..n).

% specify the number of position 

position(1..n).

% each position has exactly one person 

1 {seat(P,S): person(P) } 1 :- position(S). 

% each person occupies only one seat 

:- person(P), position(P1), position(P2), neq(P1,P2), 
   seat(P,P1), seat(P,P2).

% removing seating arrangement where there is a 
% pair of 'dislike' persons seating next to 
% each other 

:- person(P), person(Q), position(SP), 
   dislike(P, Q), seat(P, SP), P < n, seat(Q, SP+1).

:- person(P), person(Q), 
   dislike(P, Q), seat(P, n), seat(Q, 1).

:- person(P), person(Q), position(SP), 
   dislike(P, Q), seat(P, SP), SP > 1, seat(Q, SP-1).

:- person(P), person(Q), 
   dislike(P, Q), seat(P, 1), seat(Q, n).

%% this is where you change the instance 

dislike(1,2). 

% the following declarations make the reading of 
% the stable model easier 

hide position(P).  % hide atoms of the form position(X) from output 
hide person(P).  % hide atoms of the form person(X) from output