clear(X, res(puton(_A,B),S)) :-
    (clear(X,S), (X\==B)); X=table.

clear(Z, res(pickup(X,Y),S)) :-
    block(Z),
    block(X),
    block(Z) \= block(X),
    (Z = Y ; clear(Z,S)).

on(X,Y,res(puton(A,B),State)) :-
    (X=A,Y=B);
    on(X,Y,State).

on(X,Y,res(pickup(A,_B),State)) :-
    on(X,Y,State), X\==A.

poss(pickup(X,Y),State) :-
    clear(X,State), on(X,Y,State).

holding(X, res(pickup(X,Y),State)) :-
    poss(pickup(X,Y),State).

poss(puton(X,Y), res(pickup(X,Z),State)) :-
    holding(X,res(pickup(X,Z),State)),clear(Z,res(pickup(X,Z),State)).