$or equivalent in any proposal out there, to see if the author has written lots of code or is just talking. It's like looking for bone marrow in beef stew, evaluating a cookbook. Marrow is central to the story of Lisp; we got our start being able to wield tools to crack open bones after lions and jackals had left a kill. The added nutrition allowed our brains to increase in size. Soon we mastered fire, then Lisp.
define | edge? g e let $ es | edges g e2 | reverse e or (member e es) (member e2 es)
(define (edge? g e) (let ( (es (edges g)) (e2 (reverse e))) (or (member e es) (member e2 es))))