 Since both these quantities are derived from the same quantity "x"("s"–1) (which terminates the preceding era), in accordance with the formula "k"("s") + "x"("s") = 1/"x"("s"–1), their [[Probability distribution|statistical distribution]]s cannot be regarded as independent.The joint distribution "W""s"("k","x")"dx" of both quantities can be obtained from the distribution "w""s"–1("x")"dx" by making in the latter the substitution "x" → 1/("x" + "k").In other words, the function "W""s"("k","x") is given by the very expression under the summation sign in the right side of .