Consider the problem of determining whether two trees have the same fringe: the same set of leaves in the same order, regardless of internal structure. An obvious way to solve this problem is to write a function flatten that takes a tree as argument and returns an ordered list of its leaves. Then we can say
(define same-fringe
    (lambda (T1 T2)
        (equal (flatten T1) (flatten T2))))
Write a straightforward version of flatten in Scheme. How efficient is same-fringe when the trees differ in their first few leaves? How would your answer differ in a language like Haskell, which uses lazy evaluation for all arguments? How hard is it to get Haskell’s behavior in Scheme, using delay and force?