From the NannyMUD documentation

LAST CHANGE

2000-12-19

FUNCTION

NAME
        _prev_obj - Give the previous object.


SYNTAX
	object _prev_obj(object obj)

DESCRIPTION
	Given an object, this returns the previous object in the main
	object list.


NOTE
	The main list is treated as circular, i.e. if you give the first
	object in the list, you will be given the last.