“…One of the most fundamental concepts in the quantum description of nature is that of entanglement [1,2,3,4,5], which in recent years has been the subject of intense research efforts (see, for instance, the following, by no means exhaustive list of references: [1,2,3,4,5,6,7,8,9,10]). A state of a composite quantum system is called "entangled" if it cannot be represented as a mixture of factorizable pure states.…”