solve(Start, ActionList) :-
   depthfirst([Start], [], RevActionList), reverse(RevActionList, ActionList).

depthfirst([State | States], ActionList, ActionList) :-
   goal(State).

depthfirst([State | States], ActionList, FinalActions) :-
   successor(State, Action, NewState),
   \+ visitedBefore(NewState, [State | States]),
   depthfirst([NewState, State | States], 
              [Action | ActionList], FinalActions).
	 

reverse([], []).
reverse([Head|Tail], Reversed) :- reverse(Tail, Revtail),
                                  append(Revtail, [Head], Reversed).

append([], Xs, Xs).
append([X|Xs], Ys, [X|Zs]) :- append(Xs, Ys, Zs).

visitedBefore(X, [Y|Ys]) :- sameState(X, Y).
visitedBefore(X, [Y|Ys]) :- visitedBefore(X, Ys).