+ Some comments comparing this exercise to *The Little Schemer*, and Scheme more generally:
+
+ * The `set_equal?` you're trying to define here is like `eqset?` in Chapter 7 of *The Little Schemer*, and `set_cons x xs` would be like `(makeset (cons x xs))`, from that same chapter.
+ * `mem?` and `without` are like the `member?` and `rember` functions defined in Chapter 2 and 3 of *The Little Schemer*, though those functions are defined for lists of symbolic atoms, and here you are instead defining them for lists of numbers. *The Little Schemer* also defines `multirember`, which removes all occurrences of a match rather than just the first; and `member*` and `rember*` in Chapter 5, that operate on lists that may contain other, embedded lists.
+ * The native Scheme function that most resembles the `mem?` you're defining is `memv`, though that is defined for more than just numbers, and when that `memv` finds a match it returns a *list* starting with the match, rather than `#t`.
+