A counterexample to the Erd\H{o}s--S\'os bipartite-link conjecture
Erd\H{o}s and S\'os conjectured that every $n$-vertex $3$-uniform hypergraph whose link graphs are all bipartite has at most $(1/4+o(1))\binom n3$ edges. We disprove this conjecture by constructing counterexamples with edge density at least $0.250000356>1/4$ for all sufficiently large $n$.