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Published online by Cambridge University Press: 26 February 2010
Let 1 ≤ α ≤ β ≤ γ be cardinals, and let
denote the class of all graphs on γ vertices having no subgraph isomorphic to Kα,β. A graph
is called universal if every
can be embedded into Go as a subgraph. We prove that, if α < ω ≤ γ and the General Continuum Hypothesis is assumed, then
has a universal element, if, and only if, (i) γ > ω or (ii) γ = ω, α = 1 and β ≤ 3. Using the Axiom of Constructibility, we also show that there does not exist a universal graph in
.