code: def _case_insensitive_zone_lookup(zone):
      """case-insensitively matching timezone, else return zone unchanged"""
      global _all_timezones_lower_to_standard
      if _all_timezones_lower_to_standard is None:
          _all_timezones_lower_to_standard = dict(
              (tz.lower(), tz) for tz in _all_timezones_unchecked
          )  # noqa
      return _all_timezones_lower_to_standard.get(zone.lower()) or zone
  
imports: import sys
  import datetime
  import os.path
  from pytz.exceptions import AmbiguousTimeError
  from pytz.exceptions import InvalidTimeError
  from pytz.exceptions import NonExistentTimeError
  from pytz.exceptions import UnknownTimeZoneError
  from pytz.lazy import LazyDict, LazyList, LazySet
  from pytz.tzinfo import unpickler, BaseTzInfo
  from pytz.tzfile import build_tzinfo
label_desc: Use image node_id 5 for calling a global function with example usage: _case_insensitive_zone_lookup(zone) and returns: unknown