Here is a mysterious data declaration:

data Song $=$ Harmony Song Song

$|$ Atom String

deriving $($Show$,$ Eq$)$

Hint $(?)$: You can think of a Song as a tree having branches named Harmony, and leaves named

Atom, where the leaves contain strings.

By being sung, a Song changes according to the following $$rules$$:

$1.$ If the song is a Harmony whose left child is a Harmony whose left child is Atom x where the

first character of x is $$K$,$ the song becomes the right child of the left child of the root.

Viewed as trees