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diff --git a/hints/assignment_4_hint_3.mdwn b/hints/assignment_4_hint_3.mdwn
index 48063d3a..9cfef8ad 100644
--- a/hints/assignment_4_hint_3.mdwn
+++ b/hints/assignment_4_hint_3.mdwn
@@ -1,2 +1,26 @@
-Hints for enumerating a tree's fringe.
+Hints for Y1,Y2. 
+
+*	Begin by trying to define `X1` and `X2` directly, then once they're working, you can abstract back to a pair of combinators `Y1` and `Y2` that generate `X1` and `X2` for a given pair of arguments `T1` and `T2`.
+
+	You want:
+
+		X1 <~~> T1 X1 X2 and
+		X2 <~~> T2 X1 X2
+
+*	X1 is presumably going to have some form like:
+
+		(\elem1 elem2 ... (T1
+							(do-something-with-the-elems-to-make-X1)
+							(do-something-with-the-elems-to-make-X2)
+						  ))
+		some-elem1 some-elem2 ...
+	
+	Right? What will the form of X2 be?
+
+*	Can you see how to go on?
+
+*	Call the displayed abstract above `(\elem1 elem2 ... (...))` "elem0". What's the relation between `X1`, `elem0`, `elem1`, `elem2`...?
+
+*	Go on, now you can do it.
+