At the siyium tonight we learnt that this explanation is brought down on the last page of the Chavos Yair (IIRC) in the name of a Rav Oppenheimer. > > On 2/7/07, SBA <sba at sba2.com> wrote: > > 9 years out of the 40 Tish'sh B'Av fell on Shabbat, and as they were not > > allowed to dig graves on Shabbat, we have 37 - 9 = 28 years.