Following McKay [796] , an ensamble X is a triple (x,A X ,P X ), where x is the value of a random variable, which takes on one of a set of possible values, A X~f a 1 ,a 2 ,:::,a i ,:::,a N g, having probabilities P X~f p 1 ,p 2 ,:::,p N g, with p(x~a i )~p i , p i §0 and X a i [A X p(x~a i )~1.