A TVS X with continuous dual space ${\displaystyle X^{\prime }}$  is said to be countably barrelled if ${\displaystyle B^{\prime }\subseteq X^{\prime }}$  is a weak-* bounded subset of ${\displaystyle X^{\prime }}$  that is equal to a countable union of equicontinuous subsets of ${\displaystyle X^{\prime }}$ , then ${\displaystyle B^{\prime }}$  is itself equicontinuous.^[1] A Hausdorff locally convex TVS is countably barrelled if and only if each barrel in X that is equal to the countable intersection of closed convex balanced neighborhoods of 0 is itself a neighborhood of 0.^[1]

σ-barrelled space edit

A TVS with continuous dual space ${\displaystyle X^{\prime }}$  is said to be σ-barrelled if every weak-* bounded (countable) sequence in ${\displaystyle X^{\prime }}$  is equicontinuous.^[1]

Sequentially barrelled space edit

A TVS with continuous dual space ${\displaystyle X^{\prime }}$  is said to be sequentially barrelled if every weak-* convergent sequence in ${\displaystyle X^{\prime }}$  is equicontinuous.^[1]

Every countably barrelled space is a countably quasibarrelled space, a σ-barrelled space, a σ-quasi-barrelled space, and a sequentially barrelled space.^[1] An H-space is a TVS whose strong dual space is countably barrelled.^[1]

Every countably barrelled space is a σ-barrelled space and every σ-barrelled space is sequentially barrelled.^[1] Every σ-barrelled space is a σ-quasi-barrelled space.^[1]

A locally convex quasi-barrelled space that is also a 𝜎-barrelled space is a barrelled space.^[1]

Every barrelled space is countably barrelled.^[1] However, there exist semi-reflexive countably barrelled spaces that are not barrelled.^[1] The strong dual of a distinguished space and of a metrizable locally convex space is countably barrelled.^[1]

Counter-examples edit

There exist σ-barrelled spaces that are not countably barrelled.^[1] There exist normed DF-spaces that are not countably barrelled.^[1] There exists a quasi-barrelled space that is not a 𝜎-barrelled space.^[1] There exist σ-barrelled spaces that are not Mackey spaces.^[1] There exist σ-barrelled spaces that are not countably quasi-barrelled spaces and thus not countably barrelled.^[1] There exist sequentially barrelled spaces that are not σ-quasi-barrelled.^[1] There exist quasi-complete locally convex TVSs that are not sequentially barrelled.^[1]

• Barrelled space
• H-space
• Quasibarrelled space

• Khaleelulla, S. M. (1982). Counterexamples in Topological Vector Spaces. Lecture Notes in Mathematics. Vol. 936. Berlin, Heidelberg, New York: Springer-Verlag. ISBN 978-3-540-11565-6. OCLC 8588370.
• Narici, Lawrence; Beckenstein, Edward (2011). Topological Vector Spaces. Pure and applied mathematics (Second ed.). Boca Raton, FL: CRC Press. ISBN 978-1584888666. OCLC 144216834.
• Schaefer, Helmut H.; Wolff, Manfred P. (1999). Topological Vector Spaces. GTM. Vol. 8 (Second ed.). New York, NY: Springer New York Imprint Springer. ISBN 978-1-4612-7155-0. OCLC 840278135.
• Trèves, François (2006) [1967]. Topological Vector Spaces, Distributions and Kernels. Mineola, N.Y.: Dover Publications. ISBN 978-0-486-45352-1. OCLC 853623322.
• Wong (1979). Schwartz spaces, nuclear spaces, and tensor products. Berlin New York: Springer-Verlag. ISBN 3-540-09513-6. OCLC 5126158.