Given a locally compact group and a -space? , one can consider the category of -equivariant sheaves on . It has been understood by Joseph Bernstein and Valery Lunts that the derived category of the abelian category of equivariant sheaves (or of any other abelian category) is not the most sensible choice, when the action is not free. Instead one needs to use -resolutions, i.e. to effectively consider resolutions of the space itself while defining the derived category.