%   OCTOPUS Axioms in Prolog

%  Action Precondition Axioms.

poss(startMove(H,X,Y,T,T1),S) :- start(S,T), clear(X,S), clear(Y,S),
       not X = Y, not reserved(X,S), not reserved(Y,S), hand(H), 
       not handInUse(H,S), moveDuration(H,X,Y,S,D), T1 is T + D.

poss(startMoveToTable(H,X,T,T1),S) :- start(S,T), clear(X,S),
        not ontable(X,S), not reserved(X,S), hand(H), not handInUse(H,S),
        moveToTableDuration(H,X,S,D), T1 is T + D.

poss(endMove(H,X,Y,T,T1),S) :- moving(H,X,Y,T,T1,S),
                           precedesActiveProcessTerminationTimes(T1,S).

poss(endMoveToTable(H,X,T,T1),S) :- movingToTable(H,X,T,T1,S),
                           precedesActiveProcessTerminationTimes(T1,S).

%  Successor State Axioms.

clear(X,do(A,S)) :- (A = startMove(H,Y,Z,T,T1) ;
                      A = startMoveToTable(H,Y,T,T1)), on(Y,X,S) ;
                    A = endMove(H,X,Z,T,T1) ;
                    A = endMoveToTable(H,X,T,T1) ;
                    clear(X,S), not A = endMove(H,Y,X,T,T1),
                    not A = startMove(H,X,Y,T,T1),
                    not A = startMoveToTable(H,X,T,T1).

on(X,Y,do(A,S)) :- A = endMove(H,X,Y,T,T1) ;
                   on(X,Y,S), not A = startMoveToTable(H,X,T,T1),
                   not A = startMove(H,X,Z,T,T1).

ontable(X,do(A,S)) :- A = endMoveToTable(H,X,T,T1) ;
                      ontable(X,S), not A = startMove(H,X,Y,T,T1).

moving(H,X,Y,T,T1,do(A,S)) :- A = startMove(H,X,Y,T,T1) ;
                moving(H,X,Y,T,T1,S), not A = endMove(H,X,Y,T,T1).

movingToTable(H,X,T,T1,do(A,S)) :- A = startMoveToTable(H,X,T,T1) ;
         movingToTable(H,X,T,T1,S), not A = endMoveToTable(H,X,T,T1).

%  Abbreviations.

handInUse(H,S) :- moving(H,X,Y,T,T1,S), ! ; movingToTable(H,X,T,T1,S).

reserved(Y,S) :- moving(H,X,Y,T,T1,S).

precedesActiveProcessTerminationTimes(T,S) :-
      not ((moving(H,X,Y,T1,T2,S) ; movingToTable(H,X,T1,T2,S)), T > T2).

%  Primitive Action Declarations.

primitive_action(startMove(H,X,Y,T,T1)).
primitive_action(endMove(H,X,Y,T,T1)).
primitive_action(startMoveToTable(H,X,T,T1)).
primitive_action(endMoveToTable(H,X,T,T1)).

%  Action Start Times.

time(startMove(H,X,Y,T,T1),T).       time(endMove(H,X,Y,T,T1),T1).
time(startMoveToTable(H,X,T,T1),T).  time(endMoveToTable(H,X,T,T1),T1).

%  Situation Start Time.

start(do(A,S),T) :- time(A,T).