Combinatorics · Oct 6, 2026

Counterexamples to Ryser’s covering conjecture

Disproves Ryser's covering conjecture by constructing intersecting (q+1)(q+1)-partite, (q+1)(q+1)-uniform hypergraphs with covering number q+1q+1, rather than the predicted bound q, for every sufficiently large prime q. A separate construction over extension fields also disproves Gyárfás's monochromatic tree-cover conjecture.

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