\documentclass[12pt]{article} \usepackage{amsmath,mathrsfs,bbm} \usepackage{amssymb} \textwidth=4.825in \overfullrule=0pt \thispagestyle{empty} \begin{document} \noindent % % {\bf L\'aszl\'o Lov\'asz} % % \medskip \noindent % % {\bf Subgraph Densities in Signed Graphons and the Local Simonovits--Sidorenko Conjecture} % % \vskip 5mm \noindent % % % % We prove inequalities between the densities of various bipartite subgraphs in signed graphs. One of the main inequalities is that the density of any bipartite graph with girth $2r$ cannot exceed the density of the $2r$-cycle. This study is motivated by the Simonovits--Sidorenko conjecture, which states that the density of a bipartite graph $F$ with $m$ edges in any graph $G$ is at least the $m$-th power of the edge density of $G$. Another way of stating this is that the graph $G$ with given edge density minimizing the number of copies of $F$ is, asymptotically, a random graph. We prove that this is true locally, i.e., for graphs $G$ that are ``close'' to a random graph. Both kinds of results are treated in the framework of graphons (2-variable functions serving as limit objects for graph sequences), which in this context was already used by Sidorenko. \end{document} .