English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We present a bound for the weak Lindel\"of number of the$G_\delta$-modification of a Hausdorff space which implies various knowncardinal inequalities, including the following two fundamental results in thetheory of cardinal invariants in topology: $|X|\le 2^{L(X)\chi(X)}$(Arhangel'skii) and $|X|\le 2^{c(X)\chi (X)}$ (Hajnal-Juhasz). This solves aquestion that goes back to Bell, Ginsburg and Woods and is mentioned in Hodel'ssurvey on Arhangel'skii's Theorem. In contrast to previous attempts we do notneed any separation axiom beyond $T_2$.

A common extension of Arhangel'skii's Theorem and the Hajnal-Juhasz inequality