On the number of unit-area triangles spanned by convex grids in the plane

Abstract

A finite set of real numbers is called convex if the differences between consecutive elements form a strictly increasing sequence. We show that, for any pair of convex sets $A, B\subset\mathbb R$, each of size $n^{1/2}$, the convex grid $A\times B$ spans at most $O(n^{37/17}\log^{2/17}n)$ unit-area triangles. This improves the best known upper bound $O(n^{31/14})$ recently obtained in \cite{RS}. Our analysis also applies to more general families of sets $A$, $B$, known as sets of Szemer\'edi--Trotter type.