Let$\DeclareMathOperator\len{len}\DeclareMathOperator\Tor{Tor}$Let $A$$(A,\mathfrak{m})$ be a regular local ring, and $x \in \mathcal{m}^2$$x \in \mathfrak{m}^2$ be a non-zero prime element. So $R:=A/(x)$ is a non-regular Cohen-Macaulay local domain.
By Eisenbud's famous work "Homological algebra on a complete intersection, with an application to group representations", the (infinite) minimal free resolution of any finitely generated $R$-module $M$ becomes periodic of period at most $2$ after at most $\dim R$ steps.
For two finitely generated $R$-module $M, N$ such that $Tor_i^R(M,N)$$\Tor_i^R(M,N)$ has finite length for all $i$, we define their PoincarePoincaré series as
$P_{M,N}(t)=\sum_{i=0}^{\infty}len_{R}(Tor_i^R(M,N))t^{i}$$P_{M,N}(t)=\sum_{i=0}^{\infty}\len_{R}(\Tor_i^R(M,N))t^{i}$.
By Eisenbud's result, $P_{M,N}(t)$ is a rational function with only possible poles at $t=1$. We then define the Euler characteristic as $\chi(M,N):=P_{M,N}(-1)$.
Questions: has such generalized Euler characteristic been studied before? Is it well-behaved e.g satisfying usual properties of Euler characteristic? Do we know analogs of Serre's homological conjecture for it?
