If there is a mapping that is closed and open, is that enough to claim that that mapping is continuous? I can't really prove that or disprove that.
Is this mapping continuous?
2 Answers
No. Example: the floor function $x\mapsto\lfloor x\rfloor$, from $(\Bbb{R},\vert\cdot\vert)$ to $\Bbb{Z}$ (with the discrete topology) is both open and closed, but the preimage of $\{1\}$ (an open set under the discrete topology) is $[1,2)$, which is not open under $\vert\cdot\vert$.
In fact any map to a space endowed with the discrete topology will always be both open and closed. Continuity is still possible though, just not guaranteed. For example a constant function like $f:(\Bbb{R},\vert\cdot\vert)\rightarrow(\Bbb{R},2^\Bbb{R})$ with $x\mapsto 1$; the preimage of any set containing $1$ is $\Bbb{R}$, which is open, while the preimage of any set not containing $1$ is empty, also open. So this map is continuous.
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0See edited post. – 2012-12-14
Take any nonempty set $X$, and let $(X, d)$ be the discrete space and $(X, \tau)$ the indiscrete space. The identity from the latter to the former is both closed and open, but not continuous.