Intersections of several disks of the Riemann sphere as K-spectral sets

Catalin Badea, Bernhard Beckermann, Michel Crouzeix

We prove that if $n$ closed disks $D_1,D_2,...,D_n$, of the Riemann sphere are spectral sets for a bounded linear operator $A$ on a Hilbert space, then their intersection $D_1\c…