On non-proper intersections and local intersection numbers

Abstract

Given pure-dimensional (generalized) cycles ${\mu }_1$ and ${\mu }_2$ on a complex manifold $Y$ we introduce a product ${\mu }_1{\diamond }_Y{\mu }_2$ that is a generalized cycle whose multiplicities at each point are the local intersection numbers at the point. % If $Y$ is projective, then given a very ample line bundle $L\to Y$ we define a product $μ_1\bl μ_2$ whose multiplicities at each point also coincide with the local intersection numbers. In addition, provided that ${\mu }_1$ and ${\mu }_2$ are effective, this product satisfies a Bézout inequality. If $i\colon Y\to \Pk^N$ is an embedding such that $i^*\Ok(1)=L$, then $μ_1\bl μ_2$ can be expressed as a mean value of Stückrad-Vogel cycles on $\Pk^N$. There are quite explicit relations between $\di_Y$ and $\bl$.