This explanation looks like it was lifted with little modification from The Little Schemer - a book that cannot be recommended enough.
Similarly there is "A Little Java, A Few Patterns", that one teaches Java, and is written by the same authors.
I was so excited about these books that I started writing "The Little C", it's gonna teach C the same way schemer books teach lisp!
PS. I always give proper attribution. You missed "My derivation is based on the one in "The Little Schemer" book."
PPS. The Little Schemer explains very little about what's going on. I explain all the steps in details.
PPPS. Books are meant to be quoted, re-interpreted, and re-stated.