The problem became significant in the early development of set theory.
Also, his book on set theory became a standard introduction to the field.
Several ways have been proposed to define the natural numbers using set theory.
It is a proposed alternative to the standard set theory.
The following example provides a more useful application of near set theory.
This line of thought, again, leads to small set theories.
Cantor's work between 1874 and 1884 is the origin of set theory.
The basic concepts of set theory are now used throughout mathematics.
Note that this definition cannot be expressed in the language of set theory itself.
It is an important tool in effective descriptive set theory.