anchor.diff:     case local_to_utc(LocalDateTime, TimezoneFrom) of
         Date = {{_,_,_},{_,_,_}} ->
            utc_to_local(Date, TimezoneTo);
  +      [{{_,_,_},{_,_,_}},{{_,_,_},{_,_,_}}] ->
  +         ambiguous;
         Res ->
            Res
      end.
  
positive.code:             is_not_in_dst ->
                 LocalDateTime;
              ambiguous_time ->
                 RecheckIt = adjust_datetime(LocalDateTime, DstShift),
                 case localtime_dst:check(RecheckIt, TzRule) of
                    ambiguous_time ->
                       RecheckIt;
                    _ ->
                       LocalDateTime
                 end
           end
     end.
  
  % local_to_utc(LocalDateTime, Timezone) -> UtcDateTime | tim_not_exists | {error, ErrDescr}
  %  LocalDateTime = DateTime()
  %  Timezone = String()
  %  UtcDateTime = DateTime()
  %  ErrDescr = atom(), unknown_tz
  local_to_utc(LocalDateTime, Timezone) ->
     case lists:keyfind(get_timezone(Timezone), 1, ?tz_database) of
  
negative.code:          case localtime_dst:check(LocalDateTime, TzRule) of
              is_in_dst ->
                 adjust_datetime(UtcDateTime, invert_shift(DstShift));
              is_not_in_dst ->
                 UtcDateTime;
              ambiguous_time ->
                 [UtcDateTime, adjust_datetime(UtcDateTime, invert_shift(DstShift))];
              time_not_exists ->
                 time_not_exists
           end
     end.
  
  % local_to_local(LocalDateTime, TimezoneFrom, TimezoneTo) -> LocalDateTime | ambiguous | time_not_exists | {error, ErrDescr}
  %  LocalDateTime = DateTime()
  %  TimezoneFrom = String()
  %  TimezoneTo = String()
  