**Q.** “Do these two sets partitioning a boundary have a common name?” 

**A.** Yes. They are the *rims* of $A$ and its complement.

**Q.** “Who studied them?”

**A.** Kar-Ping Shum

**References**

1. [2017 Shum](http://www.mathtransit.com/cornucopia/2017_shum_a.php) 
2. [1996 Shum](http://www.mathtransit.com/cornucopia/1996_shum_a.php)
3. [1993 Shum](http://www.mathtransit.com/cornucopia/1993_shum_a.php)
4. [1975 Shum and Yip](http://www.mathtransit.com/cornucopia/1975_sy_a.php)