Property B

In mathematics, Property B is a certain set theoretic property. Formally, given a finite set X, a collection C of subsets of X, all of size n, has Property B if we can partition X into two disjoint subsets Y and Z such that every set in C meets both Y and Z. The smallest number of sets in a collection of sets of size n such that C does not have Property B is denoted by m(n).

The property gets its name from mathematician Felix Bernstein, who first introduced the property in 1908.