Exercise 3.5.1

Question

Argue that a set $A$ is a $G_{\delta}$ set if and only if its complement is an $F_{\sigma}$ set.

Ulisse Mini · Accepted Answer

If $A$ is a $G_\delta$ set, then $A^c$ is a $F_\sigma$ set by De Morgan's laws.
  Likewise if $A$ is an $F_\sigma$ set then $A^c$ must be a $G_\delta$ set.

Exercise 3.5.1

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Exercise 3.5.1

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