Now that you understand how Lisp handles true and false, let’s look at
if and some of the other conditional commands.
if command can be used to make different things happen when things are true (such as when 1 + 2 = 3) or false (such as when 1 + 2 = 4).
(if (= (+ 1 2) 3)
(if (= (+ 1 2) 4)
if command can also be used to check whether a list is empty:
So far, the only way to branch on a condition that we’ve looked at has been the
(if (oddp 5)