Question 66
For which of the sets $A = \mathbb{R}$ or $A = \mathbb{Q}$ is there a function $f : A \to (0, +\infty)$ such that $\forall x_1, x_2 \in A,\ x_1 \neq x_2$ the condition $\min\{f(x_1), f(x_2)\} \leq |x_1 - x_2|$ is satisfied?
(Andrii Anikushin)
(Andrii Anikushin)