code: def check_schedule():
      
      all_items = prefetch_schedule_items()
      for validator, _type, _msg in SCHEDULE_ITEM_VALIDATORS:
          if validator(all_items):
              return False
  
      all_slots = prefetch_slots()
      for validator, _type, _msg in SLOT_VALIDATORS:
          if validator(all_slots):
              return False
      return True
docs: Helper routine to easily test if the schedule is valid