Modifications of the "central-method" to construct Steiner triple systems

Publisher Summary The chapter describes modifications of the “central-method” to construct steiner triple systems. Let V with IVI = v be a finite set and B a set of 3-subsets of V. The elements of V are called points, those of B lines. If any 2-subset of V is contained in exactly one line, then the pair ( V, B ) is called a Steiner triple system of order v, in short STS(v). The condition v = 7, 9 + 6n, n E No, is necessary and sufficient for the existence of STS(u) (the trivial cases v = 1, v = 3 are excluded). The set of these “admissible” numbers, of these “Steiner numbers” is denoted by STS.