Steiner system

An $S (𝑡, 𝑘, 𝑛)$ Steiner system is a set $Ω$ of $𝑛$ points, together with a set of $𝑘$ -element subsets $𝐵 \subseteq P (Ω)$ , called blocks or $𝑘$ -ads, such that any set of $𝑡$ points is contained in exactly one $𝑘$ -ad. #m/def/comb Excluding trivial systems, $1 < 𝑡 < 𝑘 < 𝑛$ .