anchor.diff:  %% must be sorted.
   
   init_vars(Vs) ->
  -    sort([{V,0,0} || {var,V} <- Vs]).
  +    vdb_new(Vs).
   
   new_vars([], _, Vdb) -> Vdb;
   new_vars([V], I, Vdb) -> vdb_store_new(V, {V,I,I}, Vdb);
  
positive.code: 
  add_var(V, F, L, Vdb) ->
      vdb_store_new(V, {V,F,L}, Vdb).
  
  vdb_find(V, Vdb) ->
      case lists:keyfind(V, 1, Vdb) of
  
negative.code:     [ if L >= Max -> {V,F,locked};
  	 true -> Vd
        end || {V,F,L}=Vd <- Vdb, F < Min, L >= Min ].
  