 Conversely, for a right "D""X"-module "N", 
is a right "D""Y"-module.Since this mixes the right exact tensor product with the left exact pushforward, it is common to set instead
Because of this, much of the theory of "D"-modules is developed using the full power of homological algebra, in particular derived categories.It can be shown that the Weyl algebra is a (left and right) Noetherian ring.