# Tag Info

1

Definitely not. Just think about that the universal set of input is a decidable language, but there are infinite subsets of it are undecidable...

4

From the definition you gave, the supersets have to be removed, as you want to keep only those sets for which there is no proper subset in $\mathcal{F}$. For example: In blue are the sets of $\mathcal{F}$ which don't have proper subsets in $\mathcal{F}$, in red are the ones who do. You want to keep the blue ones, by definition of $\pi$.

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