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  • 1 Alfréd Rényi Institute of Mathematics 1053 Budapest Reáltanoda u. 13-15 Hungary
  • 2 Eötvös University Department of Computer Science 1518 Budapest P.O.Box 120 Hungary
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Abstract  

We determine a class of triple systems such that each must occur in a triple system with uncountable chromatic number that omits

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(the unique system consisting of two triples on four vertices). This class contains all odd circuits of length ≧ 7. We also show that consistently there are two finite triple systems such that they can separately be omitted by uncountably chromatic triple systems but not both.

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