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Let $G$ be arbitrary group. Let us assume it is $\operatorname{FP}_\infty$. Suppose that the integral cohomology groups $H^i(G, \mathbb{Z})$ have bounded rank as finitely generated free abelian groups for all $i \geq 0$, i.e. exists $N \geq 0$ such that $\mathrm{rk}_{\mathbb{Z}}H_i(G, \mathbb{Z}) \leq N$ for every $i \geq 0$. Is there name for this property? Of course each $H^i(G, \mathbb{Z})$ is finitely generated (but not necessarily with upper bound on their ranks across all $i$) as $G$ is $\operatorname{FP}_\infty$ but I am interested in this (apparantly) stronger property. Is it equivalent to $\operatorname{FP}_\infty$? Is there a group of type $\operatorname{FP}_\infty$ which is not of this type? I am equally interested in the homology case $H_i(G, \mathbb{Z})$.

Obviously free groups have this stronger property as do torsion-free hyperbolic groups, and any group of type $\operatorname{FP}$.

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    $\begingroup$ Easy example of an $FP_{\infty}$ group with unbounded ranks of (co)homology is $(\mathbb Z/2)^2$. Also you can take square of Thompson group (or some other one having nontrivial homology in every/"most" degrees) for unbounded ranks of rational homology. $\endgroup$
    – Denis T
    Commented Apr 25, 2023 at 21:37
  • $\begingroup$ @DenisT Yes, that makes sense. Is there a standard name for this stronger property? $\endgroup$ Commented Apr 26, 2023 at 20:43
  • $\begingroup$ Well, people have studied groups G with stronger property: ones which have a periodic flat/injective resolution of R over RG. One may ask just for periodic cohomology; for infinite groups those are not equivalent. Reference for finite groups are several Swan's papers from late 50s-early 60s ("Periodic Resolutions for Finite Groups", 1960 is pretty comprehensive). I'm not an expert in those matters, but I recall that people who are doing Galois theory and modular representation theory of algebraic groups are sometimes interested in nontrivial modules with periodic resolutions $\endgroup$
    – Denis T
    Commented Apr 26, 2023 at 22:02

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