infinite-range=

(defmethod infinite-range= ((range-1 cons) (range-2 infinite-range))
  (with-slots (x-increment y-increment) range-2
    ; for cell (a, b) in range (pn, qn)
    ; (a, b) is in (pn, qn)
    ; if any of these are true:
    ;   a = b = p = q = 0
    ;   a = p = 0 and b mod q = 0 and b/q > 0
    ;   b = q = 0 and a mod p = 0 and a/p > 0
    ;   None of a, b, p or q = 0 and a mod p = 0 and b mod q = 0 and a/p = b/q and a/p > 0 and b/q > 0
    (let ((p x-increment)
      (q y-increment)
      (a (car range-1))
      (b (cdr range-1)))
      (or
       (= a b p q 0)
       (and (= a p 0) (zerop (mod b q)) (plusp (/ b q)))
       (and (= b q 0) (zerop (mod a p)) (plusp (/ a p)))
       (and (not (zerop a))
        (not (zerop b))
        (not (zerop p))
        (not (zerop q))
        (zerop (mod a p))
        (zerop (mod b q))
        (plusp (/ a p))
        (plusp (/ b q))
        (= (/ a p) (/ b q)))))))