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IMO 2010 — Complete Shortlist Question 1

IMO Shortlist · IMO 2010 — Complete Shortlist

Question 1

Determine all functions $f: \mathbb{R} \rightarrow \mathbb{R}$ such that the equality

$$
f([x] y)=f(x)[f(y)] .
$$

holds for all $x, y \in \mathbb{R}$. Here, by $[x]$ we denote the greatest integer not exceeding $x$.