PPT Slide
Cond is the most general conditional provided by Lisp.
( <test1> <consequents 1> )
( <test2> <consequents 2> )
( <testm> <consequents m> )
-- Each test is a predicate that returns NIL (false) or nonNIL (any nonNIL value acts like true).
-- Each consequent is zero or more Lisp forms (usually one).
-- The tests are tried sequentially. As soon as one succeeds, all of its consequent forms are evaluated, and the value of the last consequent form is returned by the cond.
-- If all the tests yield NIL, the cond returns NIL.