As stated in Section 3.2, in a continuous distribution the values of a p.d.f. can be changed arbitrarily at any countable set of points. Therefore, for such a distribution it would be more precise to state that the random variables X and Y are independent if and only if it is possible to choose versions of the p.d.f.’sf, f_1.and f_2 such that Eq. (3.5.5) is satisfied for -∞