1. Mathematics
2. Calculus and Analysis
3. Real Analysis
4. 27188

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Definition: A set A subset or equal to R is called an F_&(F sigma) set if it can be written as the countable union of closed sets. A set B subset or equal to R is called G_&(G sigma) if it can be written asthe countable intersection of open sets.

1-Argue that a set A is a G_& (G sigma) set if and only if its complement is an F_& (F sigma)set