TheoremsForFree.scala

def fa[A0,A1](a: A0): A1 = ???
def head[A](l: List[A]): A = l.head
def fmap[A,B](f: A => B)(l: List[A]): List[B] = l.map(f)
"head and then map is the same as map and then head" {
    fa[A0,A1] compose head[A0] == head[A1] compose fmap[A0,A1](fa)
}

def tail[A](l: List[A]): List[A] = l.tail

"tail and then map is the same as map and then tail" {
    fa[A0,A1] compose tail[A0] == tail[A1] compose fmap[A0,A1](fa)
}