L20_A
Riemann Sum (二變數函數的黎曼和)
Fubini's Theorem (富比尼定理)
iterated integrals (重積分)
[Double integrals over general regions] (二變數函數在一般區域上的積分)

L20_B
[Double integrals over general regions] (Conti.) (續.二變數函數在一般區域上的積分)
17.3 The evaluation of double integrals by repeated integrals