anchor.diff:  
   union_decorate(U1, U2, Opaques) ->
     Union = union_decorate(U1, U2, Opaques, 0, []),
  -  [A,B,F,I,L,N,T,M,_,_R,Map] = U1,
  -  [_,_,_,_,_,_,_,_,Opaque,_,_] = U2,
  +  [A,B,F,I,L,N,T,M,_,Map] = U1,
  +  [_,_,_,_,_,_,_,_,Opaque,_] = U2,
     List = [A,B,F,I,L,N,T,M,Map],
     DecList = [Dec ||
                 E <- List,
  
positive.code:   end.
  
  unify_union(List) ->
    [A,B,F,I,L,N,T,M,O,R,Map] = List,
    if O =:= ?none -> no;
      true ->
        S = t_opaque_structure(O),
        {yes, t_sup([A,B,F,I,L,N,T,M,S,R,Map])}
    end.
  
  -spec is_opaque_type(erl_type(), [erl_type()]) -> boolean().
  
negative.code: 	 %% t_maybe_improper_list/2,
  	 t_product/1,
  	 t_reference/0,
  	 t_string/0,
  	 t_struct_from_opaque/2,
  	 t_subst/2,
  