anchor.diff:  
   bit_types([]) ->
       [];
  -bit_types([Atom | Rest]) when atom(Atom) ->
  +bit_types([Atom | Rest]) when is_atom(Atom) ->
       [Atom | bit_types(Rest)];
  -bit_types([{Atom, Integer} | Rest]) when atom(Atom), integer(Integer) ->
  +bit_types([{Atom, Integer} | Rest]) when is_atom(Atom), is_integer(Integer) ->
       [{Atom, Integer} | bit_types(Rest)].
   
   
  
positive.code: form({attribute,Line,import,{Mod,Is0}}) ->
      Is1 = farity_list(Is0),
      {attribute,Line,import,{Mod,Is1}};
  form({attribute,Line,compile,C}) ->
      {attribute,Line,compile,C};
  form({attribute,Line,record,{Name,Defs0}}) ->
  
negative.code: farity_list([{Name,Arity}|Fas]) ->
      [{Name,Arity}|farity_list(Fas)];
  farity_list([]) -> [].
  
  %% -type variable_list([Var]) -> [Var]
  
  variable_list([{var,Line,Var}|Vs]) ->
      [{var,Line,Var}|variable_list(Vs)];
  variable_list([]) -> [].
  
  %% -type record_defs([RecDef]) -> [RecDef].
  %%  N.B. Field names are full expressions here but only atoms are allowed
  