We introduce a new homological invariant called quasi-projective dimension, which is
a generalization of projective dimension. We discuss various properties of
quasi-projective dimension. Among other things, we prove the following. (1) Over a
quotient of a regular local ring by a regular sequence, every finitely generated
module has finite quasi-projective dimension. (2) The Auslander–Buchsbaum
formula and the depth formula for modules of finite projective dimension
remain valid for modules of finite quasi-projective dimension. (3) Several
results on vanishing of Tor and Ext hold for modules of finite quasi-projective
dimension.
Dedicated to Professors Roger and
Sylvia Wiegand on the occasion of their 150th
birthday