Paul Hudak answers a question concerning mutations of unshared structures:
>George, I think you are implying that if an unshared list is passed to
>this function then it can be mutated instead of copied. But
>determining that it is unshared can be very difficult (of course it is
>undecideable
>George, I think you are implying that if an unshared list is passed to
>this function then it can be mutated instead of copied. But
>determining that it is unshared can be very difficult (of course it is
>undecideable in general). Note in particular that you have to
>determine if any
