Beginning exercises from chapter 13 of programming in haskell.
exercise 1 - overlapping pattern.
exercise 2 - proof by induction on add
exercise 3 - commutativity.
exercise 4 - all (== x) (replicate n x) - proof by induction.
exercise 5
Removing exercise
exercise 6 - proof of map (f . g) x
format
publish draft for chapter 13
take'n drop
Proof on (leaves t - nodes t) = 1.
Last exercise.
Publishing chapter 12 in blog