Counting lemma for octahedrally quasirandom three-uniform hypergraphs

ID: counting-lemma-for-octahedrally-quasirandom-three-uniform-hypergraphs

Let a fixed simple three-uniform hypergraph have hypergraph edges, with one host vertex of a hypergraph class for each vertex of a hypergraph. Assume each hypergraph edge triple has indicator , subset density , and balanced three-dimensional box norm at most . The normalized labelled hypergraph copy count is . Telescope this product against . In each error term, fix all variables outside the three vertices of a hypergraph of its balanced hypergraph edge. Every other hypergraph edge intersects that triple in at most two vertices of a hypergraph, so the remaining factors group into three pair functions bounded by one. The pair-factor correlation bound for the three-dimensional box norm bounds the error by . Summing gives
For the three-uniform tetrahedron, . The same argument with a common host set counts homomorphisms; excluding collisions of distinct abstract vertices of a hypergraph changes the count by at most .

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