anchor.diff:  %% Entry point to evaluation of the parse tree.
   materialize({query, Projections, {from, Collection}, Predicates}, State0) ->
       %% Convert collection identifier to binary.
  -    CollectionId = {list_to_binary(atom_to_list(Collection)), ?SET},
  +    CollectionId = generate_identifier(Collection),
   
       %% Materialize a dataflow graph for the predicate tree.
       {PredicateOutputId, State1} = materialize(Predicates,
  
positive.code:     ct:pal("Parse Tree: ~p", [ParseTree]),
  
      %% Create and return identifier.
      OutputId = materialize(ParseTree, #state{set_id=?DEFAULT}),
  
      %% Return output identifier.
      {ok, OutputId}.
  
negative.code: 
  %% TODO: Single projection only!
  materialize({select, Projections},
              #state{output_id=OutputId, predicate_output_id=PredicateOutputId}=State) ->
  
      %% Apply the projection.
      lasp:map(PredicateOutputId,
  