Some difficulty in the language of sets
Harold L. Schoen · The Arithmetic Teacher · 1974
A set is a well-defined collection of objects. The objects in the set, called elements, can be almost anything-people, chairs, numbers. On the surface, this is a very simple idea that is basic to all mathematics. As long as sets of physical objects are observed and manipulated, the concept remains a simple one. Difficulties begin when symbols are adopted to communicate the idea of sets and their elements. If any mathematics is to be learned from the use of sets, however, a meaningful language is necessary.