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Modular intersection graph (N=4p−1,k=2p−1,A∼B⟺∣A∩B∣=p−1)

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2026-10-14  NaN By others on same topic  0 Discussions Create my own version
For a prime number p, the vertices are k-subsets of [N]. An independent set avoids the only off-diagonal intersection congruent to k modulo p, so the Frankl-Wilson theorem bounds its size by (p−1N​). A clique has constant intersection p−1 and has size at most N, by the same theorem modulo a prime larger than k. This explicit graph gives an asymmetric Ramsey number lower bound and an exponential chromatic number lower bound.

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  • Past exam of the mathematics course of the University of Cambridge / 2003 / iii / Paper 13 / 1 / Solution
  • Past exam of the mathematics course of the University of Cambridge / 2004 / iii / Paper 13 / 5 / Solution

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