diff --git a/day01-hard/main.scm b/day01-hard/main.scm
index f7ca138..947ea07 100755
--- a/day01-hard/main.scm
+++ b/day01-hard/main.scm
@@ -25,9 +25,20 @@
 
 (define (prepend first-value) (lambda (rest) (cons first-value rest)))
 
+;=============== combinators ======================
 (define (Y f) (f (lambda (x) ((Y f) x))))
 (define (Y2 f) (f (lambda (x y) ((Y2 f) x y))))
 
+(assert-eq "Y test 1 (factorial) failed"
+  120
+  ((Y (lambda (f) (lambda (n) (if (= n 0) 1 (* n (f (- n 1))))))) 5))
+
+(assert-eq "Y2 test 1 (pascal triangle) failed"
+  35
+  ((Y2 (lambda (f) (lambda (a b)
+    (if (= a 0) 1 (if (= b 0) 1 (+ (f (- a 1) b) (f a (- b 1))))))))
+    3 4))
+
 (define (reduce-right initial reducer) (Y
   (lambda (f) (lambda (values)
     (if (null? values) initial (reducer (car values) (f (cdr values))))))))