Hard-nosed physicists are content with elementary quantum mechanics as it is. Deep searchers desire a deeper comprehension of the theory or rather of reality. Observable internal correlations in micro-system and external correlations between widely separated parts can be calculated at the office. But how can for that purpose indispensable information be observed, coded and stored and transmitted in the real systems?A spectacular example is Einstein-Podolsky-Rosen entanglement. 'How can one part know what has been or will be happening at the other distant part?'.