Yes, as has been pointed out, he is missing a pair of commas (or more correctly, a patch to ensure that v is evaluated once and only once --- right now it is ev

Yes, as has been pointed out, he is missing a pair of commas (or more correctly, a patch to ensure that v is evaluated once and only once --- right now it is evaluated 0 times, and adding 2 commas would make it eval twice. Using the definition of (square x) is the cleanest way to fix this).