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+++ b/assignment10.mdwn
@@ -9,6 +9,25 @@
 	>	it with.
 
 
+	As Ken Shan points out, this is an instance of the algorithm
+	for converting name/year citations (like 'v. Montague 1970')
+	to numerals corresponding to their ('v. [24]').  Except that
+	bibliograpic numerals don't start with zero.
+
+	Give some thought to efficiency: there are straightforward
+	solutions that involve traversing the tree once (in order to,
+	say, construct a suitable mapping from leafs to ints), then
+	traversing it again to do the conversion.  Can you find a
+	solution that traverses the tree exactly once, replacing each
+	leaf as soon as you see it?
+
+	Consider a variation in which you must replace each leaf with
+	is number of occurrences in the tree.  Is there any way to do
+	that with a single traversal?
+
+	You can assume that the tree is leaf-labeled (no labels on the
+	internal nodes), and that the leafs are, say, chars.
+
 	Here is [a hint](/hints/assignment_10_hint).