The Tor functors 
are the left derived functors of the module
tensor product of a right module 
and a left module 
over a unit ring 
. If 
is a projective resolution by right modules,
then
 |
The zeroth Abelian group is 
, while the higher Abelian
groups measure the failure of module tensor
product to preserve exact sequences. For positive integers 
and 
,
for example,
 |
