Function collision
= Function collision
{title2=$x\neq x',\quad f(x)=f(x')$}
A function collision is a pair of distinct inputs $x\neq x'$ with $f(x)=f(x')$. An <injective function> has no collisions. For a two-to-one function every nonempty <fiber> has two elements and hence one unordered collision pair. Finding such a pair through an oracle is the task of <quantum collision finding>.