Uniquely 3-colourable Steiner triple systems
نویسندگان
چکیده
منابع مشابه
Uniquely circular colourable and uniquely fractional colourable graphs of large girth
Given any rational numbers r ≥ r′ > 2 and an integer g, we prove that there is a graph G of girth at least g, which is uniquely circular r-colourable and uniquely fractional r′-colourable. Moreover, the graph G has maximum degree bounded by a number which depends on r and r′ but does not depend on g.
متن کاملA Note on Uniquely H-colourable Graphs
For a graph H, we compare two notions of uniquely H-colourable graphs, where one is defined via automorphisms, the second by vertex partitions. We prove that the two notions of uniquely H-colourable are not identical for all H, and we give a condition for when they are identical. The condition is related to the first homomorphism theorem from algebra.
متن کاملBicoloring Steiner Triple Systems
A Steiner triple system has a bicoloring with m color classes if the points are partitioned into m subsets and the three points in every block are contained in exactly two of the color classes. In this paper we give necessary conditions for the existence of a bicoloring with 3 color classes and give a multiplication theorem for Steiner triple systems with 3 color classes. We also examine bicolo...
متن کاملBalanced Steiner Triple Systems
A Steiner triple system of order v (briefly STS(v)) is a pair (X, B), where X is a v-element set and B is a collection of 3-subsets of X (triples), such that every pair of X is contained in exactly one triple of B. It is well known that a necessary and sufficient condition for a STS(v) to exist is that v#1 or 3 (mod 6). An r-coloring of a STS(v) is a map , : X [1, ..., r] such that at least two...
متن کاملUniquely D-colourable Digraphs with Large Girth
Let C and D be digraphs. A mapping f : V (D) → V (C) is a Ccolouring if for every arc uv of D, either f(u)f(v) is an arc of C or f(u) = f(v), and the preimage of every vertex of C induces an acyclic subdigraph in D. We say that D is C-colourable if it admits a C-colouring and that D is uniquely Ccolourable if it is surjectively C-colourable and any two C-colourings of D differ by an automorphis...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
ژورنال
عنوان ژورنال: Journal of Combinatorial Theory, Series A
سال: 2003
ISSN: 0097-3165
DOI: 10.1016/s0097-3165(02)00016-x