>
> Well, the right fold of `f` over a list `[a;b;c;d;e]`, using starting value z, is:
>
-> f a (f b (f c (f d (f e z))))
+> f a (f b (f c (f d (f e z))))
>
-> The left fold on the other hand starts combining `z` with elements from the left. `f z z` is then combined with `b`, and so on:
+> The left fold on the other hand starts combining `z` with elements from the left. `f z a` is then combined with `b`, and so on:
>
-> f (f (f (f (f z a) b) c) d) e
+> f (f (f (f (f z a) b) c) d) e
>
> or, if we preferred the arguments to each `f` flipped:
>
-> f e (f d (f c (f b (f a z))))
+> f e (f d (f c (f b (f a z))))
>
> Recall we implemented v3 lists as their own right-fold functions. We could
> instead implement lists as their own left-fold functions. To do that with our