%%% ZOO LANDSCAPE %%%

:- sorts
  position;
  location >> cage;
  gate.

:- variables
  P,P1                              :: position;
  L                                 :: location;
  C                                 :: cage;
  G,G1                              :: gate.

:- constants
% Each position is included in exactly one location (lmw)
  loc(position)                     :: location;
  neighbor(position,position)       :: boolean;
  side1(gate)                       :: position;
  side2(gate)                       :: position;
  opened(gate)                      :: inertialFluent.

default -neighbor(P,P1).

% Each position must have at least one neighbor (lmw)
constraint [\/P1 | neighbor(P,P1)].

% The neighbor relation is irreflexive
constraint -neighbor(P,P).

% The neighbor relation is symmetric (lmw)
constraint neighbor(P,P1) ->> neighbor(P1,P).

:- objects
% One designated location is called the outside (lmw)
  outside                           :: location.

% All other locations are cages (lmw)
constraint [\/C | L=C] where L\=outside.

% Two positions are the sides of a gate
:- constants
  sides(position,position,gate)     :: boolean.

caused sides(P,P1,G) if side1(G)=P & side2(G)=P1.
caused sides(P,P1,G) if side1(G)=P1 & side2(G)=P.
default -sides(P,P1,G).

% Each gate is associated with exactly two positions that are 
%  said to be at its sides, and these positions must belong to 
%  different locations  (lmw)
constraint loc(side1(G))\=loc(side2(G)).

% No two gates have the same two sides
constraint sides(P,P1,G) & sides(P,P1,G1) ->> G=G1.

% Two positions are neighbors if they are the sides of a gate
constraint sides(P,P1,G) ->> neighbor(P,P1).

% Two positions in different locations are neighbors only if 
%  they are the two sides of a gate
constraint loc(P)\=loc(P1) & neighbor(P,P1) 
                  ->> [\/G | sides(P,P1,G)].