P a simple charge and f:X->R => expected value of f w.r.t. P, * Ep(f)=Sum(X in support(P), f(x)P(x)) If X is a random variable: * Ex(f)=Sum(a in support(P), f(a)Px(a)) with f:X->R * Ex=Sum(a in support(P), aPx(a))