What a set is

Set theory is the language in which all of mathematics is formalised. Venn diagrams are the most intuitive way to visualise its objects and operations.

Definition — Set

A set is a collection of objects, called elements, that are well defined and distinct. It is denoted by capital letters ($A, B, C,\ldots$).

Every set is represented by a region of the plane enclosed in a circle; the rectangle containing everything is the universal set $U$.

Three sets $A$, $B$, $C$ inside the universe $U$: the overlaps show the shared elements.

Links

Topics: Set theory
Concepts: Venn diagram · Set
People: John Venn