If we gave you such a `Y1` and `Y2`, how would you implement the above definitions of `even` and `odd`?
-<LI>(More challenging.) Using our derivation of Y from the [[Week2]] notes as a model, construct a pair `Y1` and `Y2` that behave in the way described.
+<LI>(More challenging.) Using our derivation of Y from the [Week3 notes](/week3/#index4h2) as a model, construct a pair `Y1` and `Y2` that behave in the way described.
(See [[hints/Assignment 4 hint 4]] if you need some hints.)