More generally, one can look at the question of defining:formula_3for real-number values of "a" in such a way that when "a" takes an integer value "n", the usual power of "n"-fold differentiation is recovered for "n" > 0, and the −"n"th power of "J" when "n" < 0.
More generally, one can look at the question of defining the linear functional:formula_3for real-number values of "a" in such a way that when "a" takes an integer value, "n", the usual power of "n"-fold differentiation is recovered for "n" > 0, and the −"n"th power of "J" when "n" < 0.