  Communication
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# S and L spaces

In mathematics, S-spaces and L-spaces are certain topological spaces, believed to be dual to each other in some sense. 

## Justin T. Moore

Justin Tatch Moore (born 1974) is a set theorist and logician.

## Lindelöf space

In mathematics, a Lindelöf space is a topological space in which every open cover has a countable subcover.

## Martin's axiom

In the mathematical field of set theory, Martin's axiom, introduced by, is a statement that is independent of the usual axioms of ZFC set theory.

## Number theory

Number theory, or in older usage arithmetic, is a branch of pure mathematics devoted primarily to the study of the integers.

## Proper forcing axiom

In the mathematical field of set theory, the proper forcing axiom (PFA) is a significant strengthening of Martin's axiom, where forcings with the countable chain condition (ccc) are replaced by proper forcings.

## Stevo Todorčević

Stevo Todorčević is a Canadian-French-Serbian mathematician, one of the world’s leading logicians.

## Topological space

In topology and related branches of mathematics, a topological space may be defined as a set of points, along with a set of neighbourhoods for each point, satisfying a set of axioms relating points and neighbourhoods.

## Zermelo–Fraenkel set theory

In mathematics, Zermelo–Fraenkel set theory, named after mathematicians Ernst Zermelo and Abraham Fraenkel, is an axiomatic system that was proposed in the early twentieth century in order to formulate a theory of sets free of paradoxes such as Russell's paradox.

## References

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