How QCD evolution kernels depend on the type of evolution variable

We show that by changing the upper phase space limit in calculation of an evolution kernel, one can change its functional form. This happens already at the NLO level, e.g. when the upper phase space limit is defined in terms of maximum of transverse momenta. The upper phase space limit of the evolution kernel corresponds to the evolution variable used in a Parton Shower, and this dependence means that the different kernels need to be used depending on the ordering of the Parton Shower.