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Singh
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Betti numbers of a Cohen-Macaulay Module in small projective dimension

I am trying to compute the Betti numbers of some Stanley-Reisner ring $R_\delta$, where the underlying complex $\Delta$ is shellable and the projective dimension of the $R_\delta$ is $3\text{ or }4$. I have the following information about the minimal free resolution of $R_\delta$:

  1. The resolution has two twists at first level and then it is pure, i.e. $\beta_{1, j}\neq 0$ iff $j=j_1$ and $j=j_2$ for some $j_1\neq j_2$ and $\beta_{i,j}\neq 0$ for unique values of $j$ if $i\geq 2$.

  2. I know all shiftings, i.e. values of $j$ when $\beta_{i, j}\neq 0$.

  3. I also know the values of $\beta_{1, j_1}$ and $\beta_{1, j_1}$.

Is it possible to compute all other Betti numbers then? I am interested in something similar to Herzog-Kuhl equation.

Singh
  • 179
  • 6