> We need to re-identify yo and yi because after split(x) we have two  > versions of each: one in the x_inner and another in x_tail    If we get rid of the `clone` in `splitWithTail`, we wouldn't have to re-identify yo and yi. They should be pointing to the ones in `x_inner` as before the split. The ones in `x_tail` should be the ones created new.  