Not all of the arithmetic encodings are so neat and elegant, however. As we mentioned, `pred` takes some ingenuity. We'll also have you define `zero?` and <code>≤</code> for homework.
-Here is an example of [some programmers having fun with Church numbers](http://www.schemers.org/Miscellaneous/imagine.txt).
+Here is an example of [some programmers having fun with Church numbers](http://www.schemers.org/Miscellaneous/imagine.txt). A tiny glossary: FORTRAN is a very old imperatival language that Scheme hoped to replace; SML is a sister language to OCaml; Chez is one Scheme implementation (like Racket and Chicken); and you will learn about "Y" next week. You should be able to figure out what the refrain means.