1. A.B. Goncharov, Multiple polylogarithms, cyclotomy and modular complexes, Math. Res. Lett.5 (1998) 497 [arXiv:1105.2076] [INSPIRE].
2. K.T. Chen, Iterated path integrals, Bull. Amer. Math. Soc.83 (1977) 831.
3. A.V. Kotikov, L.N. Lipatov, A.I. Onishchenko and V.N. Velizhanin, Three loop universal anomalous dimension of the Wilson operators in N = 4 SUSY Yang-Mills model, Phys. Lett.B 595 (2004) 521 [Erratum ibid.B 632 (2006) 754] [hep-th/0404092] [INSPIRE].
4. J.M. Henn and B. Mistlberger, Four-gluon scattering at three loops, infrared structure and the Regge limit, Phys. Rev. Lett.117 (2016) 171601 [arXiv:1608.00850] [INSPIRE].
5. S. Abreu et al., The two-loop five-point amplitude in
$$ \mathcal{N} $$ = 4 super-Yang-Mills theory, Phys. Rev. Lett.122 (2019) 121603 [arXiv:1812.08941] [INSPIRE].