A minor quibble I know, but every time I use sets I want to add/subtract single elements to/from them. There is no function provided for doing this, so instead you have to do union/delete with a singleton set constructed from the element. I appreciate the zeal of the designer of this module to construct the smallest possible interface (I wish the same person had designed the standard Prelude) but I think this zeal is overdone. You do often need to operate with single elements. After all, if you wanted real hair-shirt minimalism you should get rid of "elementOf" (replace it by \el set -> isEmptySet (intersect set (singletonSet el)), but no-one would seriously suggest that - I hope.