=+18.4. The assumption of J-finiteness in Theorem 18.2 is essential: Let u be Lebesgue measure on the line, let v be counting measure on the line, and take E=[(x, y): x=y]. Then (18.1) and (18.2) do not agree.

18.5. Example 18.2 in effect connects T as the area of the unit disk D, with the ₸

of trigonometry.