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GeezerVison is showing mathworld.wolfram.com — Pure Semisimplicity Conjecture -- from Wolfram MathWorld

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Pure Semisimplicity Conjecture


The pure semisimplicity conjecture asserts that a right pure semisimple ring has only finitely many isomorphism classes of indecomposable right modules. All these modules are finitely generated in this setting. This is the finite representation type condition, and the conjecture is equivalent to requiring every right pure semisimple ring to be left pure semisimple (Šaroch 2021).

Ren (2026) reported a counterexample, an upper triangular ring

 R=(H T; 0 T),

where H is a division subring of a division ring T and the upper-right entry is the natural H-T bimodule. Ren (2026) claims that R is right pure semisimple but neither left pure semisimple nor of finite representation type. Ren (2026) supplies an accompanying Lean development stating the counterexample with the module-theoretic definitions. The claimed refutation remains subject to independent assessment. Ren (2026) reports GPT-6 Astra assistance with the construction and proof, and GPT-6.1 Sol and Claude Opus 5.5 assistance with formalization.

Generalov and Tursunbaev (2026) report another counterexample of this triangular form. They construct a division ring E by adjoining a shift s to the division ring of fractions of a rational algebra with generators x_i for i in Z and relations [x_(i+1),x_i]=1 and [x_i,x_j]=0 for |i-j|>1. The shift satisfies sx_is^(-1)=x_(i+1). Taking the division subring generated over Q by x_(-1) and x_1s as the upper-left entry gives a hereditary ring claimed to be right pure semisimple with infinitely many isomorphism classes of indecomposable right modules.


See also

Pure Semisimple Ring, Semisimple Ring

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References

Generalov, A. I. and Tursunbaev, A. "Division Ring Extensions and a Counterexample to the Pure Semisimplicity Conjecture." 6 Nov 2026. https://arxiv.org/abs/2611.09749v1.Ren, J. "A Counterexample to the Pure Semisimplicity Conjecture." 29 Oct 2026. https://arxiv.org/abs/2610.39883.Šaroch, J. "Pure Semisimplicity Conjecture and Artin Problem for Dimension Sequences." J. Pure Appl. Algebra 225, 106745, 2021. https://doi.org/10.1016/j.jpaa.2021.106745.

Cite this as:

Weisstein, Eric W. "Pure Semisimplicity Conjecture." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/PureSemisimplicityConjecture.html

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