anchor.diff:  %  Sign = term(), '+', '-'
   %  Hours = Minutes = Integer(),
   %  {Shift, DstShift} - returns, when shift is ambiguous
  +%  ErrDesc = atom(), unknown_tz
   tz_shift(_UtcDateTime, "UTC") ->
      0;
   tz_shift(LocalDateTime, Timezone) ->
  
positive.code: %  UtcDateTime = DateTime()
  %  Timezone = String()
  %  LocalDateTime = DateTime()
  %  ErrDescr = unknown_tz
  utc_to_local(UtcDateTime, Timezone) ->
     case lists:keyfind(get_timezone(Timezone), 1, ?tz_database) of
        false ->
  
negative.code: %  LocalDateTime = DateTime()
  %  TimezoneFrom = String()
  %  TimezoneTo = String()
  %  ErrDescr = atom(), unknown_tz
  local_to_local(LocalDateTime, TimezoneFrom, TimezoneTo) ->
     case local_to_utc(LocalDateTime, TimezoneFrom) of
        Date = {{_,_,_},{_,_,_}} ->
  