User:Danhorsley/STS

In mathematics, a Steiner triple system is a block design consisting of a set of points together with a collection of triples of these points such that every pair of points appears together is precisely one triple.

Definition
Formally a Steiner triple system is a pair (V,B) where V is a set and B is a multiset of 3-element subsets of V (called triples) such that each 2-element subset of V is contained in exactly one triple in B.