From the colour glass condensate to filamentation: systematics of classical Yang–Mills theory Owe Philipsen, Björn Wagenbach and Savvas Zafeiropoulos Eur. Phys. J. C, 79 4 (2019) 286 Published online: 28 March 2019 DOI: 10.1140/epjc/s10052-019-6790-8