Surfaces that are covered by two pencils of circles

Abstract

We list up to Möbius equivalence all possible degrees and embedding dimensions of real surfaces that are covered by at least two pencils of circles, together with the number of such pencils. In addition, we classify incidences between the contained circles, complex lines and isolated singularities. Such geometric characteristics are encoded in the Néron–Severi lattices of such surfaces and is of potential interest to geometric modelers and architects. As an application we confirm Blum’s conjecture in higher dimensional space and we address the Blaschke–Bol problem by classifying surfaces that are covered by hexagonal webs of circles. In particular, we find new examples of such webs that cannot be embedded in 3-dimensional space.