The double-soft integral for an arbitrary angle between hard radiators Fabrizio Caola, Maximilian Delto, Hjalte Frellesvig and Kirill Melnikov Eur. Phys. J. C, 78 8 (2018) 687 Published online: 29 August 2018 DOI: 10.1140/epjc/s10052-018-6180-7