/********************************************************
%% testing data %%

:- dynamic dyn/1, dy/1.
dyn(current_state(4)).
dyn(change((1, 2), (1,2), [], [dy(add2), dy(rubbish2) ])).
dyn(change((2, 2), (2,2), [], [dy(add2a)])).
dyn(change((2, 3), (2,3), [], [dy(add3) ] )).
dyn(change((3, 3), (3,3), [dy(rubbish2)], [dy(add3a) ] )).
dyn(change((3, 4), (3,4), [], [dy(add4) ] )).

dy(original).
dy(add2).
dy(add2a).
dy(add3).
dy(add3a).
dy(add4).

***** testing area ****

[model].
find_model_path(1, 4, Path).
dyn(S).
dy(X).
roll_back_one_step((3,4)).
top_roll_back(1).
top_roll_back(2).
top_roll_back(3).

***************************************************************/