+
+2. Do the same with crossy lists. That is, given an arbitrary type
+'a, let the boxed type be a list of objects of type 'a. The singleton
+is `\p.[p]`, and the composition operator is
+
+ >=> (first:P->[Q]) (second:Q->[R]) :(P->[R]) = fun p -> [r | q <- first p, r <- second q]
+
+Sanity check:
+
+ f p = [p, p+1]
+ s q = [q*q, q+q]
+ >=> f s 7 = [49, 14, 64, 16]
+
+3. Do the same for zippy lists. That is, you need to find a
+composition operator such that
+
+ f p = [p, p+1]
+ s q = [q*q, q+q]
+ >=> f s 7 = [49, 16]
+
+and then prove it obeys the monad laws.