:- use_module(library(lists)).

precond(pickup(X),[ontable(X),clear(X),handempty]).
del(pickup(X),[ontable(X),clear(X),handempty]).
add(pickup(X),[holding(X)]).

precond(putdown(X),[holding(X)]).
del(putdown(X),[holding(X)]).
add(putdown(X),[ontable(X),clear(X),handempty]).

precond(stack(X,Y),[holding(X),clear(Y)]).
del(stack(X,Y),[holding(X),clear(Y)]).
add(stack(X,Y),[on(X,Y),clear(X),handempty]).

precond(unstack(X,Y),[on(X,Y),clear(X),handempty]).
del(unstack(X,Y),[on(X,Y),clear(X),handempty]).
add(unstack(X,Y),[holding(X),clear(Y)]).

applicabile(OP,S):-
	precond(OP,Prec),
	holds(Prec,S).
	
holds([],S).
holds([G|RG],S):- member(G,S), holds(RG,S).

trasforma(A,S1,S2):-
	del(A,DL),
	deleteall(S1,DL,S),
	add(A,AL),
	append(AL,S,S2).
	
deleteall(S,[],S).
deleteall(S1,[H|T],S2):- delete(S1,H,SS),
	deleteall(SS,T,S2).
	
uguale([],[]).
uguale([X|R],S):-
	member(X,S),
	delete(S,X,SS),
	uguale(R,SS).

iniziale([on(a,b),on(b,c),ontable(c),clear(a),on(d,e),on(e,f),ontable(f),clear(d),handempty]).

goal([on(a,b),on(d,e),on(c,f)]).

finale(S):- goal(G), holds(G,S).