# Guided Practice 8.2

True/False: Which of the following is a valid halting measure for
`even-elements`, and why?

- the largest element of lst
- the number of distinct elements of lst
- the sum of the elements of lst
- the length of lst

## Answers:

- False. If the largest element is far down in the list, taking
(rest (rest lst)) will not change the value of the largest element.
For example, consider lst = (list 12 11 5 17 12 11). The largest
element in lst is 17, but the largest element in (rest (rest lst)) is
still 17.
- False. If the first two elements are both duplicated farther
down in the list, then taking (rest (rest lst)) will not change the
number of distinct elements.
- False. If the first two elements are both 0, then the sum of
the elements will not change.
- True. The length of a list is always a non-negative integer,
and the length decreases by two at every recursive call.

Last modified: Sun Oct 19 15:18:09 Eastern Daylight Time 2014