Definition: Subbasis and Basis of Topology

Let $(X,\mathcal O)$ be a topological space. * A basis of $(X,\mathcal O)$ is a subset $B\subseteq\mathcal O$ such that every element $O\in\mathcal O$ equals some set union of the elements of $B.$ * A subbasis of $(X,\mathcal O)$ is a subset $S\subseteq\mathcal O$ such that every element $O\in\mathcal O$ equals some set intersection of finitely many elements of $S.$

Notes

Examples

Proofs: 1
Propositions: 2


Thank you to the contributors under CC BY-SA 4.0!

Github:
bookofproofs


References

Bibliography

  1. Forster Otto: "Analysis 2, Differentialrechnung im \(\mathbb R^n\), Gewöhnliche Differentialgleichungen", Vieweg Studium, 1984
  2. Steen, L.A.;Seebach J.A.Jr.: "Counterexamples in Topology", Dover Publications, Inc, 1970
  3. Jänich, Klaus: "Topologie", Springer, 2001, 7th Edition