Signed-off-by: Jim Pryor <profjim@jimpryor.net>
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+(See [[hints/Assignment 4 hint 3]] if you need some hints.)
<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 [[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.)
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+Hints for enumerating a tree's fringe.
+