Nonplanar on-shell diagrams and leading singularities of scattering amplitudes Baoyi Chen, Gang Chen, Yeuk-Kwan E. Cheung, Yunxuan Li, Ruofei Xie and Yuan Xin Eur. Phys. J. C, 77 2 (2017) 80 Published online: 08 February 2017 DOI: 10.1140/epjc/s10052-017-4659-2