Virtual Surjection and the n-(n+1)-(n+2) Theorem for Discrete Groups

Tal Cohen, Mark Shusterman

Cohen and Shusterman prove the Fₖ and FPₖ virtual-surjection conjectures for discrete groups. Their homological fibre-product theorem assumes the common quotient Q is finitely presented; they also give counterexamples without that condition.

Sources for this record

What was already known

The k=2 virtual-surjection case and asymmetric 1-2-3 fibre-product theorem were known. Reductions left the general discrete-group cases unresolved.

AI involvement AI-centered

Cohen and Shusterman say the main arguments developed through GPT interactions. They worked out and verified every proof in detail, wrote the paper and explain the reductions.

The authors' attribution covers the paper's main arguments developed in GPT interactions, with human completion and verification.

Importance Notable

Settles the two virtual-surjection finiteness conjectures and identifies the boundary of the homological fibre-product result.

Limitations

The finite-presentation condition on Q is necessary for the stated homological fibre-product theorem. The authors report checking all proofs, but do not isolate which individual argument steps originated with GPT.

Technical verification Formal (human)

The authors explicitly state that they worked out and verified all proofs, including the quotient-qualified fibre-product engine and virtual-surjection deductions. This is a completed author-side human check, not a machine formalization.

Formal checking

Worked out all proofs in detail and verified them before writing the paper

Checker
Tal Cohen and Mark Shusterman
Scope
Theorems 1.3 and 1.6 and the stated counterexample scope
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Full

The authors explain the fibre-product argument, the finite-presentability condition on Q and the known reduction that yields F_k and FP_k virtual surjection.

Correction and publication history

2026-10-18 · publication

Settles the two virtual-surjection finiteness conjectures and identifies the boundary of the homological fibre-product result.

Read this published revision