Abstract
When no single universal model for a set of structures exists at a given cardinal, then one may ask in which models of set theory does there exist a small family which embeds the rest. We show that for λ+-graphs (λ regular) omitting cliques of some finite or uncountable cardinality, it is consistent that there are small universal families and 2λ > λ+. In particular, we get such a result for triangle-free graphs.
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Thompson, K. Small universal families for graphs omitting cliques without GCH. Arch. Math. Logic 49, 799–811 (2010). https://doi.org/10.1007/s00153-010-0197-4
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DOI: https://doi.org/10.1007/s00153-010-0197-4