Let $ p$ be a (large) prime. How large can a set $ C\subset\mathbb F_p$ be given that there is a function $ f\colon\mathbb F_p^\times\to\mathbb F_p$ such that for every element $ g\in \mathbb F_p$ , there is at most one element $ c\in C$ with the property that $ $ g \notin \{f(z)-cz\colon z\in\mathbbRead more