I have found it useful to define `length<=?`, etc, which would naturally
extend to improper lists. I don't think it would fit well in SRFI 274,
because it is not a function between collections and collections.

One could define `length` to have start and end arguments like the ones
here, although you run into issues as to if the bounds should be
inclusive-exclusive (like the ones here) or not.

-- Peter McGoron