 Tetrahedron counting lemma

A sufficiently regular four-partite three-uniform hypergraph, supported on sufficiently regular pair cells of positive density and with positive relative triple densities, has a positive fourth-power number of three-uniform tetrahedra. On complete pair supports, telescoping the four edge functions shows that an error of at most $\xi$ in each three-dimensional box norm gives a counting error at most $4\xi$. The relative version additionally requires control of the pair-support densities.