Let $A$ be a non-meagre subset of a topological space $X$. Is $A$ comeagre in its closure $\mathcal{Cl}(A)$?
2026-03-28 01:18:45.1774660725
Is a non-meagre set comeagre in its closure?
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Not necessarily. Let $A$ be a Bernstein set in $\Bbb R$. $A$ and $\Bbb R\setminus A$ are dense in $\Bbb R$ and non-meagre. In fact, both are Baire spaces.