Recent content by jstahl

It is definitely false. Let ##X = \mathbb{R}## be the reals with the discrete topology, let ##Y = \mathbb{R}## be the reals with the Euclidean topology, and let $$ f : X\to Y\\ x\mapsto x. $$ Then ##\mathbb{Q}## is dense in ##Y##, but ##\overline{f^{-1}(\mathbb{Q})} = \overline{\mathbb{Q}}...