diff --git a/welcome-back-to-dr-racket/main.rkt b/welcome-back-to-dr-racket/main.rkt
index 737998c..03c42c3 100644
--- a/welcome-back-to-dr-racket/main.rkt
+++ b/welcome-back-to-dr-racket/main.rkt
@@ -1,28 +1,31 @@
 ;; The first three lines of this file were inserted by DrRacket. They record metadata
 ;; about the language level of this file in a form that our tools can easily process.
 #reader(lib "htdp-beginner-reader.ss" "lang")((modname main) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
-; List of Number -> String
+; Number a, Number b, Number c -> String
 ; Determines whether a list of 3 numbers is ascending or descending. Throws error if neither.
-(define (scending-how l)
-  (cond [(< (first l) (second l) (third l)) "ascending"]
-        [(> (first l) (second l) (third l)) "descending"]
+(define (scending-how a b c)
+  (cond [(< a b c) "ascending"]
+        [(> a b c) "descending"]
         [else (error "too complex")]))
 
-(check-expect (scending-how (list 1 2 3)) "ascending")
-(check-expect (scending-how (list 5 4 3)) "descending")
-(check-error (scending-how (list 1 0 3)))
+(check-expect (scending-how 1 2 3) "ascending")
+(check-expect (scending-how 5 4 3) "descending")
+(check-error (scending-how 1 0 3))
 
 
-; Number, Number -> Number
+; Number a, Number b -> Number
 ; Finds two positive numbers' greatest common denominator.
 (define (gcd2 a b)
   (cond
     [(= a 0) b]
     [(= b 0) a]
-    [(= 0 (+ (modulo a 2) (modulo b 2))) (* 2 (gcd2 (/ a 2) (/ b 2)))]
-    [(= 0 (modulo b 2)) (gcd2 a (/ b 2))]
-    [(= 0 (modulo a 2)) (gcd2 (/ a 2) b)]
-    [else (if (<= a b) (gcd2 a (- b a)) (gcd2 b (- a b)))]))
+    [(and (even? a) (even? b))
+     (* 2 (gcd2 (/ a 2) (/ b 2)))]
+    [(even? b) (gcd2 a (/ b 2))]
+    [(even? a) (gcd2 (/ a 2) b)]
+    [else(if (<= a b)
+             (gcd2 a (- b a))
+             (gcd2 b (- a b)))]))
 
 (check-expect (gcd2 0 0) 0)
 (check-expect (gcd2 100 0) 100)
@@ -30,3 +33,13 @@
 (check-expect (gcd2 10 10) 10)
 (check-expect (gcd2 14 7) 7)
 (check-expect (gcd2 288 64) 32)
+
+; (gcd2 30 210)
+; (* 2 (gcd2 15 105))
+; (* 2 (gcd2 15 90))
+; (* 2 (gcd2 15 45))
+; (* 2 (gcd2 15 30))
+; (* 2 (gcd2 15 15))
+; (* 2 (gcd2 15 0))
+; (* 2 15)
+; 30