set theory

joukko-oppi puhekieltä The mathematical theory of sets.
1984, Robert Goldblatt, http://ebooks.library.cornell.edu/cgi/t/text/pageviewer-idx?c=math;cc=math;idno=gold010;q1=Heyting%20algebra;view=image;seq=26;size=100;page=root Topoi, the categorial analysis of logic, p. 9

The above argument, known as Russell's Paradox, was discovered by Bertrand Russell in 1901. Set theory itself began a few decades earlier with the work of George Cantor.