On a depth formula for modules over local rings  
S. Choi and S. Iyengar

Abstract.
We prove that for modules M and N over a local ring R, 
the depth formula: depth M + depth N - depth R = depth 
Tor_s(M,N) - s, where s=sup{i | Tor_i(M,N) is non-zero}, 
holds under certain conditions. This adds to the list 
cases where the depth formula, which extends the classical 
Auslander-Buchsbaum equality, is satisfied.