General topology

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In mathematics, general topology or point-set topology is the branch of topology which studies elementary properties of topological spaces and structures defined on them.

1 History
2 Scope
3 See also
4 Standard references

History

General topology grew out of a number of areas, most importantly the following:

the detailed study of subsets of the real line (once known as the topology of point sets, this usage is now obsolete)
the introduction of the manifold concept
the study of metric spaces, esp. normed linear spaces, in the early days of functional analysis

It was codified, in much its form for the remainder of the twentieth century, around 1940. It captures, one might say, almost everything in the intuition of continuity, in a technically adequate form that can be applied in any area of mathematics.

Scope

More specifically, it is in general topology that basic notions are defined and theorems about them proved. This includes the following:

open and closed sets;
interior and closure;
neighbourhood and closeness;
compactness and connectedness;
continuous functions;
convergence of sequences, nets, and filters;
separation axioms
countability axioms

Other more advanced notions also appear, but are usually related directly to these fundamental concepts, without reference to other branches of mathematics. Set-theoretic topology examines such questions when they have substantial relations to axiomatic set theory, as is often the case.

Other main branches of topology are algebraic topology, geometric topology, and differential topology. As the name implies, general topology provides the common foundation for these areas.