“…For the congruent number elliptic curve with such N, the L-function L(E, s) does not usually vanish at s = 1, and it is known that the quantity M(E) = L(E, 1)/Ω is a rational number, where Ω denotes the smallest positive real period of E. The conjecture of Birch and Swinnerton-Dyer (1) predicts that, for these N, the rational number M(E) must always be divisible by 4 k , and Zhao (14,15) found an ingenious proof of this fact. This divisibility plays a central role in Tian's work (2). Both Tian (2) and Zhao (14,15) use induction on the number k of odd prime divisors of N in their work, and it is intriguing to note that there are some striking parallels between the averaging of Heegner points attached to divisors of N used by Tian (2), and the averaging of the values M(E) over divisors of N used by Zhao (14,15), in their separate proofs.…”