Definition:G-Delta Set

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Let $T = \left({S, \tau}\right)$ be a topological space.

A $G_\delta$ set (G-delta set) is a set which can be written as a countable intersection of open sets of $T$.

Also see

  • Results about $G_\delta$ sets can be found here.

Linguistic Note

The name $G_\delta$ originates from the German:

G for Gebiet, which is German for area or neighborhood (used in the sense open set in this case)
$\delta$ (Greek d) for Durchschnitt, which is German for set intersection.