anchor.diff:    [];
   sequence([T], Acc, _Delimiter) ->
     lists:flatten(lists:reverse([T|Acc]));
  -sequence([T|Left], Acc, Delimiter) -> 
  -  sequence(Left, [T ++ Delimiter|Acc], Delimiter).
  +sequence([T|Ts], Acc, Delimiter) ->
  +  sequence(Ts, [T ++ Delimiter|Acc], Delimiter).
   
   %%=============================================================================
   %% 
  
positive.code: t_is_none_or_unit(_) -> false.
  
  %%-----------------------------------------------------------------------------
  %% Atoms and the derived type bool
  %%
  
  -spec t_atom() -> erl_type().
  
negative.code: %% Unification
  %%
  
  -type t_unify_ret() :: {erl_type(), [{_, erl_type()}]}.
  
  -spec t_unify(erl_type(), erl_type()) -> t_unify_ret().
  
  t_unify(T1, T2) ->
    t_unify(T1, T2, []).
  
  -spec t_unify(erl_type(), erl_type(), [erl_type()]) -> t_unify_ret().
  
  t_unify(T1, T2, Opaques) ->
    {T, Dict} = t_unify(T1, T2, dict:new(), Opaques),
  