THE FINITISTIC DIMENSION CONJECTURE AND RELATIVELY PROJECTIVE MODULES

The famous finitistic dimension conjecture says that every finite-dimensional K-algebra over a field K should have finite finitistic dimension. This conjecture is equivalent to the following statement: If B is a subalgebra of a finite-dimensional K-algebra A such that the radical of B is a left ideal in A, and if A has finite finitistic dimension, then B has finite finitistic dimension. In the paper, we shall work with a more general setting of Artin algebras. Let B be a subalgebra of an Artin algebra A such that the radical of B is a left ideal in A. (1) If the category of all finitely generated (A, B)-projective A-modules is closed under taking A-syzygies, then fin. dim(B) <= fin. dim(A) + fin. dim(BA) + 3, where fin. dim(A) denotes the finitistic dimension of A, and where fin. dim(BA) stands for the supremum of the projective dimensions of those direct summands of BA that have finite projective dimension. (2) If the extension B. A is n-hereditary for a nonnegative integer n, then gl. dim(A) <= gl.dim(B)+ n. Moreover, we show that the finitistic dimension of the trivially twisted extension of two algebras of finite finitistic dimension is again finite. Also, a new formulation of the finitistic dimension conjecture in terms of relative homological dimension is given. Our approach in this paper is completely different from the one in our earlier papers.