API requests

[dherman]

Doug Orleans wrote:

Cool! It'd be nice, though, if it included analogs for the rest of
the lset functions in SRFI-1, namely <=, =, adjoin, and
diff+intersection. And an emptiness test, though (= set empty) might
be enough. Oh, and (contains? set elt).

Also, might be good to state in the docs that they're amortized linear.
(Right?)

Thanks! Sorry if you've already planned to do all these, I just got
excited. :)

--Doug