Abstract
We investigate the following problem: What countable graphs must a graph of uncountable chromatic number contain? We define two graphsΓ andΔ which are very similar and we show thatΓ is contained in every graph of uncountable chromatic number, whileΔ is (consistently) not.
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Dedicated to Paul Erdős on his seventieth birthday
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Hajnal, A., Komjáth, P. What must and what need not be contained in a graph of uncountable chromatic number?. Combinatorica 4, 47–52 (1984). https://doi.org/10.1007/BF02579156
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DOI: https://doi.org/10.1007/BF02579156