Let $X$ be a compact complex nonsingular surface without curves, and $E$ a holomorphic vector bundle of rank 2 on $X$. It turns out that the associated projective bundle $\mathbf{P}E$ has no divisors if and only if $E$ is “strongly” irreducible. Using the results concerning irreducible bundles of [Banica-Le Potier, J. Crelle, 378 (1987), 1-31] and [Elencwajg- Forster, Annales Inst. Fourier, 32-4 (1982), 25-51] we give a proof of existence for bundles which are strongly irreducible.

Let $D$ be a holomorphic differential operator acting on sections of a holomorphic vector bundle on an $n$-dimensional compact complex manifold. We prove a formula, conjectured by Feigin and Shoikhet, giving the Lefschetz number of $D$ as the integral over the manifold of a differential form. The class of this differential form is obtained via formal differential geometry from the canonical generator of the Hochschild cohomology $H{H}^{2n}({𝒟}_n,{𝒟}_n^{*})$ of the algebra of differential operators on a formal neighbourhood of a...