Measurements of the strong coupling constant and the QCD colour factors using four-jet observables from hadronic Z decays. - Heister, A.; Schael, S.; Barate, R.; De Bonis, I.; Decamp, D.; Goy, C.; Lees, J.-P.; Merle, E.; Minard, M.-N.; Pietrzyk, B.; Boix, C.; Bravo, S.; et al. (European Physical Journal C -- Particles & Fields, 2003)