Repeated blocks in indecomposable twofold triple systems
نویسنده
چکیده
A Steiner triple system (STS) (a twofold triple system (TTS)) is a pair (V, B) where V is a v-set, and B is a collection of 3-subsets of V called blocks or triples such that every 2-subset of V is contained in exactly one [exactly two] blocks. The number v is called the order of the STS or TI'S. It is well-known that an STS of order v exists if and only if v 1 or 3 (mod 6), and a T r s of order v exists if and only if v ~ 0 or 1 (rood 3). A TI'S(v) (V, B) whose block-set B can be partitioned into two subsets B1, B2 such that (V, B0, (V, B2) are both STS(v)'s, is called decomposable; otherwise, it is indecomposable. An indecomposable "ITS(v) is known to exist if and only if v -= 0 or 1 (rood 3) and v :/: 3, 7 [2]. If a T r s contains two blocks bl = {x, y, z}, b2 = {x, y, z} that are identical as subsets of V then {x, y, z} is said to be a repeated block; otherwise, a block is called nonrepeated. In a recent paper [5], the author and D. Hotirnan gave a complete answer to the following question:
منابع مشابه
Repeated blocks in indecomposable twofold extended triple systems
An extended triple system (a twofold extended triple system) with no idempotent element (ETS, TETS respectively) is a pair (V, B) where V is a v-set and B is a collection of unordered triples, called blocks, of type {x,y,z} or {x,x,y}, such that each pair (whether distinct or not) is contained in exactly one (respectively, exactly two) blocks. For example, in the block {x, x, y}, the occurrence...
متن کاملThe number of repeated blocks in twofold triple systems
In this paper, we give a complete answer to the following question: Given an integer v = 0 or 1 (mod 3) and an integer k, does there exist a twofold triple system of order v with exactly k repeated triples? In particular, we prove the following theorem: If u = 0 or 4 (mod 6), D > 12. then there exists a twofold triple system of order v having exactly k repeated triples if and only if k~ I:, whe...
متن کاملPure Latin directed triple systems
It is well-known that, given a Steiner triple system, a quasigroup can be formed by defining an operation · by the identities x · x = x and x ·y = z where z is the third point in the block containing the pair {x, y}. The same is true for a Mendelsohn triple system where the pair (x, y) is considered to be ordered. But it is not true in general for directed triple systems. However directed tripl...
متن کاملCyclically Indecomposable Triple Systems that are Decomposable
Cyclically Indecomposable Triple Systems that are Decomposable Martin Grüttmüller Institut für Mathematik, Universität Rostock In this talk, we construct, by using Skolem-type and Rosa-type sequences, cyclically indecomposable two-fold triple systems TS2(v) for all admissible orders. We also investigate exhaustively the cyclically indecomposable triple systems TSλ(v) for λ = 2, v ≤ 33 and λ = 3...
متن کاملCyclic, Simple and Indecomposable Three-Fold Triple Systems
In 2000, Rees and Shalaby constructed simple indecomposable two-fold cyclic triplesystems for all v ≡ 0, 1, 3, 4, 7, and 9 (mod 12) where v = 4 or v ≥ 12, using Skolem-type sequences.We construct, using Skolem-type sequences, three-fold triple systems having theproperties of being cyclic, simple, and indecomposable for all admissible orders v, withsome possible exception...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- Discrete Mathematics
دوره 65 شماره
صفحات -
تاریخ انتشار 1987