anchor.diff:  
   tail(Pid, DataFrame, N, Keywords) ->
       gen_server:call(Pid, {'core.jun.dataframe', [DataFrame, tail, [N], 'None', Keywords]}, infinity).
  -
  -legacy_query(Pid, DataFrame, Query, _Keywords) ->
  -    [Column, Operator, Value] = jun_parser:query(Query),
  -    gen_server:call(Pid, {'core.jun', legacy_query, [DataFrame, Column, Operator, Value]}, infinity).
   
   %% Helpers
   
  
positive.code: 
  -export(['query'/4,
      head/4,
      tail/4,
      legacy_query/4]).
  
  -export([to_erl/2]).
  
  
negative.code: 
  -export([sort_values/4,
      sort_index/4]).
  
  -export([legacy_query/4,
      legacy_assignment/4]).
  
  %% DataFrames in erlang term
  to_erl(Pid, {'$erlport.opaque', python, _} = OpaqueDataFrame) ->
  