  We show how a set of POVMs, expressed as a set of $\mu$ linear maps, can be
performed with a unitary transformation followed by a von-Neumann measurement
with an ancillary system of no more than $\mu N^2$ dimensions. This result
shows that all generalized linear transformations and measurements on density
matrices can be performed by unitary transformations and von-Neumann
measurements by coupling a suitably large ancillary system.
