“…In the last several years, there has been remarkable progress in extending calculations of a number of key gauge theory quantities to the four loop level. These include the β-function [20][21][22][23], the anomalous dimensions of twist-2 operators [24][25][26][27], the cusp anomalous dimension [24,[27][28][29][30][31][32][33][34][35][36][37][38], the quark and gluon collinear anomalous dimensions [29-32, 34, 35, 35, 38-40], and most recently the full form factors [41][42][43]. These anomalous dimensions govern the behavior of scattering amplitudes and cross sections in infrared limits, allowing the resummation of logarithms that appear in these limits, and which often invalidate a fixed order perturbative expansion, to N 4 LL.…”