-15. Recursion exploiting the fold-like representation of numbers and lists (deforestation, zippers)
+15. Recursion exploiting the fold-like representation of numbers and lists ([deforestation](http://en.wikipedia.org/wiki/Deforestation_%28computer_science%29), [zippers](http://en.wikipedia.org/wiki/Zipper_%28data_structure%29))
16. General recursion using omega
17. The Y combinator(s); more on evaluation strategies
16. General recursion using omega
17. The Y combinator(s); more on evaluation strategies