<OL start=3>
<LI>blah
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+(See [[hints/Assignment 4 hint 3]] if you need some hints.)
</OL>
<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.
+
+(See [[hints/Assignment 4 hint 4]] if you need some hints.)
+
</OL>