Assumptions Underlying Bell's Inequalities
  There are several versions of Bell's inequalities, proved in different contexts, using different sets of assumptions. The discussions of their experimental violation often disregard some required assumptions and use loose formulations of others. The issue, to judge from recent publications, continues to cause misunderstandings. We present a very simple but general proof of Bell's inequalities, identifying explicitly the complete set of assumptions required. 
Angel G. Valdenebro