This one-point compactification is also known as the Alexandroff compactification after a paper by Павел Сергеевич Александров (then. The one point compactification. Definition A compactification of a topological space X is a compact topological space Y containing X as a subspace. of topological spaces and the Alexandroff one point compactification. Some prop- erties of the locally compact spaces and one point compactification are proved.

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What we have constructed is called the Alexandroff one-point compactification of the real line, discussed in more generality below. Under de Morgan duality. Let X X be a locally compact topological space. Note that a locally compact metric space is not necessarily complete, e.

## Compactification (mathematics)

A bit more formally: Relaxation in Optimization Theory and Variational Calculus. For the converse, assume that X X is Hausdorff. Let X be a Hausdorff space. com;actification

If X is locally compact, then so is any open subset U. Note however that the projective plane RP 2 is not the one-point compactification of the plane R 2 since more than one point is added. Proposition inclusion into one-point extension is open embedding Let X X be a topological space.

Proof Regarding the first point: By using this site, you agree to the Terms of Use and Privacy Policy. Definition one-point extension Let Compactificatoin X be any topological space. Proposition one-point extension of locally compact space is Hausdorff precisely if original space is Let X X be a locally compact topological space.

Warsaw circleHawaiian earring space.

## Alexandroff extension

Upon doing that, we immediately run into the problem of uniqueness, i. The methods of compactification are various, but each is a way of controlling points from “going off to infinity” by in some way adding “points at infinity” or preventing such an “escape”.

Brouwer’s fixed point theorem. Then each point in X can be identified with an evaluation function on C. K-topologyDowker space.

Embeddings into compact Hausdorff spaces may be of particular interest. Moreover, if X were compact then c X would be closed in Y and hence not dense. This example already contains the key concepts of the general case.

The map c is a Hausdorff compactification if and only if X is a locally compact, noncompact Hausdorff space. As a pointed compact Hausdorff spacethe one-point compactification compactificatoin X X may be described by a universal property:.

Thank you a lot for posting this. In the more general situation, it may not really be a compactification and hence is called the one-point extension or Alexandroff extension. Proof The unions and finite intersections of the open subsets inherited from X X are closed among themselves by the assumption that X X is a topological space.

A one-point compactification of is given by the union of two circles which are tangent to each other. Of particular interest are Hausdorff compactifications, i. If X is a Hausdorff and locally compact space which is not compact, then the Alexandroff extension Y is the pointt one-point compactification of X which is Hausdorff.

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### Compactification (mathematics) – Wikipedia

Hausdorff spaces are sober. In particular, a disjoint union of locally compact spaces is locally compact.

A topological space has a Hausdorff compactification if and only if it is Tychonoff.

For each possible “direction” in which points in R n can “escape”, one new point at infinity is added but each direction is identified with its opposite. August 12, at