Sparse ramsey graphs


IfH is a Ramsey graph for a graphG thenH is rich in copies of the graphG. Here we prove theorems in the opposite direction. We find examples ofH such that copies ofG do not form short cycles inH. This provides a strenghtening also, of the following well-known result of Erdős: there exist graphs with high chromatic number and no short cycles. In particular, we solve a problem of J. Spencer.

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Dedicated to Paul Erdős on his seventieth birthday

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Nešetřil, J., Rödl, V. Sparse ramsey graphs. Combinatorica 4, 71–78 (1984).

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AMS subject classification (1980)

  • 05 C 55
  • 05 C 38
  • 05 C 65