INACCURATE EXPERIMENTS AND ENVIRONMENT-INDUCED SUPERSELECTION RULES

It is argued that approximate superselection rules induced by the envi ronment cannot account for the emergence of definite measurement resul ts in single experiments. The reason for this is that the inaccuracy n ecessary for an experiment failing to distinguish between exact and ap proximate mixtures requires the pointer observable to be strictly clas sical. This is shown in the case that the observables of physical syst ems generate W-algebras.