Values of input parameters are never altered by PHIGS functions.
In order that any element of a list ( member of a set ), such as the set of structure names, can be inquired, in this binding the inquiry function only returns a single element of a list (member of a set ). In addition the total number of element of the list ( members of the set ) is always returned. The elements ( members ) are numbered starting from 1; each invocation of the inquiry function requires the desired element ( member ) number as an input parameter and returns the corresponding elements. When the list (set ) is empty, a zero is returned as the number of elements and the parameter representing the single element ( member ) in the list is undefined.