Investigating non-integrability and chaos in complex time

The question of integrability of systems of ordinary differential equations (ODEs) has been studied extensively for centuries. Recently, however, owing to an upsurge of interest in chaos, a lot of studies have focused on the investigation of non-integrable systems, where chaos often manifests itself as "extremely sensitive dependence on initial conditions" of a dense set of real solutions in real time. Here, we argue that non-integrability can be efficiently investigated by solving ODEs in complex time and review recent results which strongly suggest that for a system of ODEs to be non-integrable it is necessary that it possess a dense set of infinitely-sheeted solutions in the complex domain.