Math 2.0

concept

First-countable space

Summary

A topological space is first-countable when each point has a countable family of neighbourhoods that controls all neighbourhoods of the point. In such spaces, sequences are enough to describe closures and continuity.

What this node needs for W2
  • edge instance_of in: at least two examples (0 of 2)
  • edge not_instance_of in: at least one non-example (0 of 1)
  • edge specializes both: the more general notions and the special cases (0 of 1)

The writing levels say how complete the text of a node is. They do not measure its truth.

Sources

  1. Web https://en.wikipedia.org/wiki/First-countable_space, lead section

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