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MathNet 2015-part-04 — 191 problems (EN–VI) Question 177

Math Olympiad Vault · MathNet 2015-part-04 — 191 problems (EN–VI)

Question 177

Let $f : [0, 1] \to [0, 1]$ be a function with the property that for every $y \in [0, 1]$ and every $\varepsilon \gt 0$ there exists $x \in [0, 1]$ so that $|f(x) - y| \lt \varepsilon$.

a) Prove that if $f$ is continuous on $[0, 1]$, then $f$ is surjective.

b) Give an example of a function $f$ with the given property which is not surjective.