Entanglement or separability: the choice of how to factorize the algebra of a density matrixW. Thirring, R.A. Bertlmann, P. Köhler and H. NarnhoferEur. Phys. J. D, 64 2-3 (2011) 181-196DOI: https://doi.org/10.1140/epjd/e2011-20452-1