Caola, F., Henn, J. M., Melnikov, K., & Smirnov, V. A. (2014). Non-planar master integrals for the production of two off-shell vector bosons in collisions of massless partons. Journal of High Energy Physics, 2014(9), Article 043. https://doi.org/10.1007/jhep09%282014%29043