Effective descriptive set theory refines classical descriptive set theory by emphasising computability and algorithmic aspects in the study of definable sets and functions, particularly within Polish ...

According to Cantor (Mathematische Annalen 21:545—586, 1883; Cantor's letter to Dedekind, 1899) a set is any multitude which can be thought of as one ("jedes Viele, welches sich als Eines denken läßt" ...