Kochloukova–Lima homological nn-(n+1)(n+1)-(n+2)(n+2) conjecture

Let nn be a nonnegative integer, and let

1N1G1Q1,1N2G2Q11\to N_{1}\to G_{1}\to Q\to1,\qquad 1\to N_{2}\to G_{2}\to Q\to1

be short exact sequences of groups. For epimorphisms G1QG_1\to Q and G2QG_2\to Q, their fibre product is

G1×QG2={(g1,g2)G1×G2ϕ1(g1)=ϕ2(g2)}.G_{1}\times_{Q}G_{2}=\{(g_{1},g_{2})\in G_{1}\times G_{2}\mid \phi_{1}(g_{1})=\phi_{2}(g_{2})\}.

The homological nn-(n+1)(n+1)-(n+2)(n+2) conjecture. If N1N_{1} is of type FPn\operatorname{FP}_n, G1G_1 and G2G_2 are of type FPn+1\operatorname{FP}_{n+1}, and QQ is of type FPn+2\operatorname{FP}_{n+2}, then G1×QG2G_{1}\times_QG_{2} is of type FPn+1\operatorname{FP}_{n+1}. The source states that this homological conjecture implies the finiteness-property version and that the paper proves it for discrete groups under the stated hypotheses.

Sources & referencesView supporting material

Primary source

Tal Cohen and Mark Shusterman, “Virtual Surjection and the n-(n+1)-(n+2) Theorem for Discrete Groups”, arXiv:2607.18079 (2026).

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