Opposite of a Bloom Filter

Bloom filter gives a $O(1)$-efficient way to test for set memberships, but with false positives and no false negatives, i.e. it will tell you $x\in S$ while actually it is not, but not vice versa. [more]

Volume of n-ball

If we denote the Cartesian coordinate of a $n$-dimensional Euclidean space by a $n$-vector $\mathbf{x}$, then a $n$-ball centered at the origin with radius $r$ is the set of points that satisfy [more]