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In this paper, we are interested in the following question: given an arbitrary Steiner triple system S on m vertices and any 3‐uniform hypertree T on n vertices, is it necessary that S contains T as a subgraph provided m≥(1+μ)n? We show the answer is positive for a class of hypertrees and conjecture that the answer is always positive. [ABSTRACT FROM AUTHOR]

Given a 2 - ( v , k , λ ) design, S = ( X , B ) , a zero-sum n -flow of S is a map f : B ⟶ { ± 1 , … , ± ( n − 1 ) } such that for any point x ∈ X , the sum of f over all the blocks incident with x is zero. It has been conjectured that every Steiner triple system, STS ( v ) , on v points ( v > 7 ) admits a zero-sum 3 -flow. We show that for every pair ( v , λ ) for which a triple system, TS ( v , λ ) , exists, there exists one which has a zero-sum 3 -flow, except when ( v , λ ) ∈ { ( 3 , 1 ) , ( 4 , 2 ) , ( 6 , 2 ) , ( 7 , 1 ) } . We also give a O ( λ 2 v 2 ) bound on n and a recursive result which shows that every STS ( v ) with a zero-sum 3 -flow can be embedded in an STS ( 2 v + 1 ) with a zero-sum 3 -flow if v ≡ 3 ( m o d 4 ) , a zero-sum 4 -flow if v ≡ 3 ( m o d 6 ) and with a zero-sum 5 -flow if v ≡ 1 ( m o d 4 ) . [ABSTRACT FROM AUTHOR]

Abstract: Franek et al. recently described four constructions for large sets of -intersecting Steiner triple systems of order (STS ) [F. Franek, M.J. Grannell, T.S. Griggs, A. Rosa, On the large sets of -intersecting Steiner triple systems of order , Des. Codes Cryptogr. 26 (2002) 243–256]. In this study we focus on large sets of -intersecting STS . Some recursive constructions are presented that involve three-wise balanced designs. By applying these constructions we obtain some new infinite classes of such large sets, and the large sets of -intersecting KTS are used to produce some new large sets of Kirkman triple systems. [Copyright &y& Elsevier]

A family ( X, B), ( X, B), ..., ( X, B) of q STS( υ)s is a λ-fold large set of STS( υ) and denoted by LSTS( υ) if every 3-subset of X is contained in exactly λ STS( υ)s of the collection. It is indecomposable and denoted by IDLSTS( υ) if there does not exist an LSTS( υ) contained in the collection for any λ′ < λ. In this paper, we show that for λ = 5, 6, there is an IDLSTS( υ) for υ ≡ 1 or 3 (mod 6) with the exception IDLSTS(7). [ABSTRACT FROM AUTHOR]

Abstract: The block graph of a Steiner triple system of order v is a strongly regular graph. For large v, every strongly regular graph with these parameters is the block graph of a Steiner triple system, but exceptions exist for small orders. An explanation for some of the exceptional graphs is here provided via the concept of switching. (Group divisible designs corresponding to) Latin squares are also treated in an analogous way. Many new strongly regular graphs are obtained by switching and by constructing graphs with prescribed automorphisms. In particular, new strongly regular graphs with the following parameters that do not come from Steiner triple systems or Latin squares are found: , , , , , and . [Copyright &y& Elsevier]

Abstract: A Steiner triple system of order , STS(), may be called equivalent to another STS() if one can be converted to the other by a sequence of three simple operations involving Pasch trades with a single negative block. It is conjectured that any two STS()s on the same base set are equivalent in this sense. We prove that the equivalence class containing a given system on a base set contains all the systems that can be obtained from by any sequence of well over one hundred distinct trades, and that this equivalence class contains all isomorphic copies of on . We also show that there are trades which cannot be effected by means of Pasch trades with a single negative block. [Copyright &y& Elsevier]

Abstract: A -coloring of a graph by colors is a proper -coloring of such that in each color class there exists a vertex having neighbors in all the other color classes. The -chromatic number of a graph , denoted by , is the maximum for which has a -coloring by colors. It is obvious that . A graph is -continuous if for every between and there is a -coloring of by colors. In this paper, we study the -coloring of Kneser graphs and determine for some values of and . Moreover, we prove that is -continuous for . [Copyright &y& Elsevier]

Abstract: The concept of good large set of Steiner triple systems (or GLS in short) was introduced by Lu in his paper “on large sets of disjoint Steiner triple systems”, [J. Lu, On large sets of disjoint Steiner triple systems, I–III, J. Combin. Theory (A) 34 (1983) 140-182]. In this paper a doubling construction for GLSs is displayed and some existence results are obtained. [Copyright &y& Elsevier]

Abstract: A Steiner triple system (briefly ST) is in 1–1 correspondence with a Steiner quasigroup or squag (briefly SQ) [B. Ganter, H. Werner, Co-ordinatizing Steiner systems, Ann. Discrete Math. 7 (1980) 3–24; C.C. Lindner, A. Rosa, Steiner quadruple systems: A survey, Discrete Math. 21 (1979) 147–181]. It is well known that for each or 3 (mod 6) there is a planar squag of cardinality [J. Doyen, Sur la structure de certains systems triples de Steiner, Math. Z. 111 (1969) 289–300]. Quackenbush expected that there should also be semi-planar squags [R.W. Quackenbush, Varieties of Steiner loops and Steiner quasigroups, Canad. J. Math. 28 (1976) 1187–1198]. A simple squag is semi-planar if every triangle either generates the whole squag or the 9-element squag. The first author has constructed a semi-planar squag of cardinality for all and or 3 (mod 6) [M.H. Armanious, Semi-planar Steiner quasigroups of cardinality 3, Australas. J. Combin. 27 (2003) 13–27]. In fact, this construction supplies us with semi-planar squags having only nontrivial subsquags of cardinality 9. Our aim in this article is to give a recursive construction as for semi-planar squags. This construction permits us to construct semi-planar squags having nontrivial subsquags of cardinality >9. Consequently, we may say that there are semi-planar (or semi-planar ) for each positive integer and each or 3 (mod 6) with having only medial subsquags at most of cardinality (sub-) for each . [Copyright &y& Elsevier]