Modifications Necessary

• When the initial node is created.

  % start node
  node_initial(N) :-
   start_state(S),
   node_new(N),
   node_state_of(N,S),
   node_parent_of(N,-1).    <---- parent of root node=-1

• Whenever a node is expanded: an extra paramter must be provided.

  sl2nl(P,[S|Y],[N|NL]) :-
   node_new(N),
   node_state_of(N,S),
   node_parent_of(N,P),     <----- P is parent
   sl2nl(P,Y,NL).                  of all