  A simple exposition of the rarely discussed fact that a set of free boson
fields describing different, i.e. kinematically different particle types can be
quantized with mutual anticommutation relations is given by the explicit
construction of the Klein transformations changing anticommutation relations
into commutation relations. The q-analog of the presented results is also
treated. The analogous situation for two independent free fermion fields with
mutual commutation or anticommutation relations is briefly investigated.
