Rickard's Derived Morita Theory: Review and Outlook
Pith reviewed 2026-05-18 18:45 UTC · model grok-4.3
The pith
Rickard's derived Morita theorem gives a criterion for when two rings have equivalent derived module categories.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Rickard's two papers establish a Morita theory for derived categories by proving that a derived equivalence between the module categories of two rings arises from a tilting complex of bimodules, and that splendid equivalences between group algebras can be used to approach questions about blocks with abelian defect groups.
What carries the argument
Tilting complexes of bimodules, which induce equivalences between derived categories when they satisfy certain generation and orthogonality conditions.
If this is right
- Derived equivalences between rings can be verified by constructing a single tilting complex rather than exhibiting a full equivalence.
- Splendid equivalences supply a concrete strategy toward proving Broué's conjecture for blocks with abelian defect groups.
- The completion construction for triangulated categories yields a shorter route to parts of the original derived Morita theorem.
- The framework extends naturally to Morita theory for enhanced compactly generated triangulated categories in both algebraic and topological settings.
Where Pith is reading between the lines
- The completion technique might simplify computations of derived equivalences in concrete algebras beyond the cases treated by Rickard.
- The distinction between ordinary and splendid equivalences could clarify classification problems for blocks of group algebras.
- Rickard's approach suggests a template for deriving Morita-type results in other homological settings such as dg-categories.
Load-bearing premise
The survey accurately and completely presents the main results and arguments from Rickard's original papers.
What would settle it
Identifying a major theorem or argument from Rickard's papers that is omitted or misstated in this survey would show the review is incomplete.
read the original abstract
We survey the main results in Jeremy Rickard's seminal papers `Morita theory for derived categories' and `Derived equivalences and derived functors'. These papers catalysed the later development of the Morita theory of (enhanced) compactly generated triangulated categories by Keller in the algebraic setting and by Schwede and Shipley in the topological setting. We also discuss the role of Rickard's notion of splendid equivalence in the context of Brou\'e's abelian defect group conjecture, and indicate an alternative proof of parts of Rickard's Derived Morita Theorem that leverages the notion of completion of a triangulated category.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript surveys the main results of Jeremy Rickard's papers 'Morita theory for derived categories' and 'Derived equivalences and derived functors'. It asserts that these works catalysed the Morita theory of enhanced compactly generated triangulated categories developed by Keller (algebraic) and Schwede-Shipley (topological), discusses the role of Rickard's splendid equivalences in Broué's abelian defect group conjecture, and sketches an alternative proof of parts of the Derived Morita Theorem via completion of triangulated categories.
Significance. If the reproduction of Rickard's results is faithful and the alternative proof is fully developed, the survey would provide a useful historical synthesis and technical bridge between classical derived Morita theory and its extensions to compactly generated settings. The discussion of splendid equivalences in the context of Broué's conjecture adds contextual value for representation theorists.
major comments (2)
- Abstract: the catalysis claim that Rickard's papers 'catalysed' the later Morita theory of enhanced compactly generated triangulated categories by Keller and Schwede-Shipley is asserted without explicit technical lineage. No mapping is supplied showing how specific Rickard results (e.g., the Derived Morita Theorem or functorial constructions for derived equivalences) were adapted to the enhanced/compact-generator framework; a brief historical remark alone leaves the assertion as an unverified narrative rather than demonstrated continuity.
- The section indicating an alternative proof of parts of Rickard's Derived Morita Theorem via completion of a triangulated category: if this is only sketched rather than fully detailed with all steps and comparisons to the original argument, the claim of a new perspective remains unsubstantiated and requires expansion to be load-bearing for the 'Outlook' portion of the paper.
minor comments (1)
- Ensure that all references to Rickard's original papers include precise theorem or proposition numbers when summarizing their main results, to facilitate verification of faithful reproduction.
Simulated Author's Rebuttal
We thank the referee for the thoughtful report and the recommendation for major revision. We address each major comment below, agreeing where expansion is warranted to strengthen the survey and outlook sections.
read point-by-point responses
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Referee: Abstract: the catalysis claim that Rickard's papers 'catalysed' the later Morita theory of enhanced compactly generated triangulated categories by Keller and Schwede-Shipley is asserted without explicit technical lineage. No mapping is supplied showing how specific Rickard results were adapted to the enhanced/compact-generator framework.
Authors: We agree that the catalysis claim would be strengthened by a more explicit technical connection. In the revised manuscript we will add a short paragraph in the introduction mapping how Rickard's Derived Morita Theorem and tilting-complex constructions provided the functorial and compact-generator ideas later formalized in Keller's algebraic enhancement and Schwede-Shipley's topological setting. This addition will remain brief and survey-style while making the lineage concrete. revision: yes
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Referee: The section indicating an alternative proof of parts of Rickard's Derived Morita Theorem via completion of a triangulated category: if this is only sketched rather than fully detailed with all steps and comparisons to the original argument, the claim of a new perspective remains unsubstantiated.
Authors: The manuscript presents the completion-based argument as an indicative sketch rather than a complete proof, consistent with the paper's survey-and-outlook character. We accept that the 'Outlook' portion would benefit from greater substance and will expand the section with the main additional steps, a direct comparison to Rickard's original argument, and a brief discussion of where the completion approach simplifies or differs. This will be done without turning the paper into a research article. revision: yes
Circularity Check
No significant circularity: survey of external Rickard results
full rationale
The paper is a review surveying results from Rickard's external papers ('Morita theory for derived categories' and 'Derived equivalences and derived functors'). It summarizes those results, notes their historical influence on Keller and Schwede-Shipley, discusses splendid equivalences in Broué's conjecture, and mentions an alternative proof sketch using completion. No mathematical derivations, equations, fitted parameters, or predictions are presented that reduce by construction to the authors' own prior outputs. Citations to Rickard are to independent prior literature; the catalysis statement is a historical claim, not a load-bearing technical derivation internal to the paper. The work is self-contained as a survey against external benchmarks.
Axiom & Free-Parameter Ledger
Reference graph
Works this paper leans on
-
[1]
Generalized tilted algebras of typeA n
[AH81] I. Assem and D. Happel. “Generalized tilted algebras of typeA n”. Comm. Algebra9.20 (1981), pp. 2101–2125. [AHHK07] L. Angeleri H¨ ugel, D. Happel, and H. Krause, eds.Handbook of tilting theory. Vol
work page 1981
-
[2]
Mirror symmetry for del Pezzo surfaces: vanishing cycles and coherent sheaves
London Mathematical Society Lecture Note Series. Cambridge University Press, Cambridge, 2007, pp. viii+472. [AKO06] D. Auroux, L. Katzarkov, and D. Orlov. “Mirror symmetry for del Pezzo surfaces: vanishing cycles and coherent sheaves”.Invent. Math. 166.3 (2006), pp. 537–582. [Alp87] J. L. Alperin. “Weights for finite groups”. Proc. Sympos. Pure Math. 47, ...
work page 2007
-
[3]
Iterated tilted algebras of type ˜An
[AS87] I. Assem and A. Skowro´ nski. “Iterated tilted algebras of type ˜An”. Math. Z.195.2 (1987), pp. 269–290. [Aus71] M. Auslander.Representation dimension of Artin algebras. Lecture Notes. London: Queen Mary College,
work page 1987
-
[4]
Generalizations of the Bernstein- Gel′fand-Ponomarev reflection functors
[BB80] S. Brenner and M. C. R. Butler. “Generalizations of the Bernstein- Gel′fand-Ponomarev reflection functors”.Representation theory, II (Proc. Second Internat. Conf., Carleton Univ., Ottawa, Ont., 1979). Vol
work page 1979
-
[5]
Derived equivalences for the derived dis- crete algebras are standard
Lecture Notes in Math. Springer, Berlin-New York, 1980, pp. 103–169. [BC24] G. Bobinski and T. Ciborski. “Derived equivalences for the derived dis- crete algebras are standard” (Sept. 2024). arXiv:2409.05158 [math.RT]. [BCS24] T. Bozec, D. Calaque, and S. Scherotzke. “Relative critical loci and quiver moduli”.Ann. Sci. ´Ec. Norm. Sup´ er. (4)57.2 (2024), pp. 553–
-
[6]
Derived categories and Deligne-Lusztig varieties II
[BDR17] C. Bonnaf´ e, J.-F. c. Dat, and R. Rouquier. “Derived categories and Deligne-Lusztig varieties II”.Ann. of Math. (2)185.2 (2017), pp. 609–
work page 2017
-
[7]
Coherent sheaves onP n and problems in linear al- gebra
[Be˘ ı78] A. A. Be˘ ılinson. “Coherent sheaves onP n and problems in linear al- gebra”.Funktsional. Anal. i Prilozhen.12.3 (1978), pp. 68–69. REFERENCES 21 [BF78] A. K. Bousfield and E. M. Friedlander. “Homotopy theory of Γ-spaces, spectra, and bisimplicial sets”.Geometric applications of homotopy theory (Proc. Conf., Evanston, Ill., 1977), II. Vol
work page 1978
-
[8]
The preprojective algebra of a tame hereditary Artin algebra
Lecture Notes in Math. Springer, Berlin, 1978, pp. 80–130. [BGL87] D. Baer, W. Geigle, and H. Lenzing. “The preprojective algebra of a tame hereditary Artin algebra”.Comm. Algebra15.1-2 (1987), pp. 425–
work page 1978
-
[9]
Coxeter func- tors, and Gabriel’s theorem
[BGP73] I. N. Bernˇ ste˘ ın, I. M. Gel ′fand, and V. A. Ponomarev. “Coxeter func- tors, and Gabriel’s theorem”.Uspehi Mat. Nauk28.2(170) (1973), pp. 19–33. [BK90] A. I. Bondal and M. M. Kapranov. “Framed triangulated categories”. Mat. Sb.181.5 (1990), pp. 669–683. [BLL04] A. I. Bondal, M. Larsen, and V. A. Lunts. “Grothendieck ring of pre- triangulated ca...
work page 1973
-
[10]
Cat´ egories d´ eriv´ ees et vari´ et´ es de Deligne- Lusztig
1993, pp. 119–189. [BR03] C. Bonnaf´ e and R. Rouquier. “Cat´ egories d´ eriv´ ees et vari´ et´ es de Deligne- Lusztig”.Publ. Math. Inst. Hautes ´Etudes Sci.97 (2003), pp. 1–59. [Bra56] R. Brauer. “Zur Darstellungstheorie der Gruppen endlicher Ordnung”. Math. Z.63 (1956), pp. 406–444. [Bro90a] M. Brou´ e. “Isom´ etries de caract` eres et ´ equivalences de...
work page 1993
-
[11]
[Bro90b] M. Brou´ e. “Isom´ etries parfaites, types de blocs, cat´ egories d´ eriv´ ees”. Ast´ erisque181-182 (1990), pp. 61–92. [CE99] H. Cartan and S. Eilenberg.Homological algebra. Princeton Land- marks in Mathematics. Princeton University Press, Princeton, NJ, 1999, pp. xvi+390. [Che16] X.-W. Chen. “A note on standard equivalences”.Bull. Lond. Math. S...
-
[12]
Cluster tilting objects in generalized higher cluster cate- gories
[GR97] P. Gabriel and A. V. Roiter.Representations of finite-dimensional al- gebras. Springer-Verlag, Berlin, 1997, pp. iv+177. [Guo11] L. Guo. “Cluster tilting objects in generalized higher cluster cate- gories”.J. Pure Appl. Algebra215.9 (2011), pp. 2055–2071. [Hap87] D. Happel. “On the derived category of a finite-dimensional algebra”. Comment. Math. H...
work page 1997
-
[13]
Splendid derived equivalences for blocks of finite groups
London Mathematical Society Lecture Note Series. Cambridge University Press, Cambridge, 1988, pp. x+208. [Har99] M. E. Harris. “Splendid derived equivalences for blocks of finite groups”. J. London Math. Soc. (2)60.1 (1999), pp. 71–82. [Hel68] A. Heller. “Stable homotopy categories”.Bull. Amer. Math. Soc.74 (1968), pp. 28–63. [Her16] R. Hermann. “Monoidal...
work page 1988
-
[14]
Hochschild cohomology and derived Picard groups
[Kel04] B. Keller. “Hochschild cohomology and derived Picard groups”.J. Pure Appl. Algebra190.1-3 (2004), pp. 177–196. [Kel05] B. Keller. “On triangulated orbit categories”.Doc. Math.10 (2005), pp. 551–581. [Kel06] B. Keller. “On differential graded categories”.International Congress of Mathematicians. Vol. II. Eur. Math. Soc., Z¨ urich, 2006, pp. 151–
work page 2004
-
[15]
Deformed Calabi-Yau completions
London Math. Soc. Lecture Note Ser. Cambridge Univ. Press, Cambridge, 2007, pp. 49–104. REFERENCES 23 [Kel11] B. Keller. “Deformed Calabi-Yau completions”.J. Reine Angew. Math. 654 (2011), pp. 125–180. [Kel93] B. Keller. “A remark on tilting theory and DG algebras”.Manuscripta Math.79.3-4 (1993), 247?252. [Kel94] B. Keller. “Deriving DG categories”.Ann. S...
work page 2007
-
[16]
On Neeman’s well generated triangulated categories
[Kra01] H. Krause. “On Neeman’s well generated triangulated categories”. Doc. Math.6 (2001), pp. 121–126. [Kra15] H. Krause. “Deriving Auslander’s formula”.Doc. Math.20 (2015), pp. 669–688. [Kra20] H. Krause. “Completing perfect complexes”.Math. Z.296.3-4 (2020), pp. 1387–1427. [Kra22] H. Krause.Homological theory of representations. Vol
work page 2001
-
[17]
Cambridge University Press, Cam- bridge, 2022, pp
Cambridge Studies in Advanced Mathematics. Cambridge University Press, Cam- bridge, 2022, pp. xxxiv+482. [KS06a] M. Kashiwara and P. Schapira.Categories and sheaves. Vol
work page 2022
-
[18]
Notes onA ∞-algebras,A ∞-categories and non-commutative geometry
Grund- lehren der Mathematischen Wissenschaften [Fundamental Principles of Mathematical Sciences]. Springer-Verlag, Berlin, 2006, pp. x+497. [KS06b] M. Kontsevich and Y. Soibelman. “Notes onA ∞-algebras,A ∞-categories and non-commutative geometry”.Homological mirror symmetry. Vol
work page 2006
-
[19]
Twisted Hodge diamonds give rise to non-Fourier?Mukai functors
Lecture Notes in Phys. Springer, Berlin, 2006, pp. 153–219. [K¨ un24] F. K¨ ung. “Twisted Hodge diamonds give rise to non-Fourier?Mukai functors”.J. Noncommut. Geom.18.3 (2024), 891?952. [Lin98] M. Linckelmann. “On derived equivalences and local structure of blocks of finite groups”.Turkish J. Math.22.1 (1998), pp. 93–107. [Liv15] M. Livesey. “On Rouquier...
work page 2006
-
[20]
A new invariant for finite simple groups
[McK71] J. McKay. “A new invariant for finite simple groups”.Notices of the AMS (18)128 (1971), p
work page 1971
-
[21]
[Mil62] J. Milnor. “On axiomatic homology theory”.Pacific J. Math.12 (1962), pp. 337–341. [Min12] H. Minamoto. “Ampleness of two-sided tilting complexes”.Int. Math. Res. Not. IMRN1 (2012), pp. 67–101. [Miy86] Y. Miyashita. “Tilting modules of finite projective dimension”.Math. Z.193.1 (1986), pp. 113–146. [Mor58] K. Morita. “Duality for modules and its ap...
work page 1962
-
[22]
Princeton University Press, Princeton, NJ, 2001, pp
Annals of Mathematics Studies. Princeton University Press, Princeton, NJ, 2001, pp. viii+449. [Nee18] A. Neeman.The categoriesT c andT b c determine each other
work page 2001
-
[23]
Metrics on triangulated categories
arXiv:1806.06471 [math.CT]. [Nee20] A. Neeman. “Metrics on triangulated categories”.J. Pure Appl. Alge- bra224.4 (2020), pp. 106206,
-
[24]
On auto-equivalences and complete derived invariants of gentle algebras
[Nee90] A. Neeman. “The derived category of an exact category”.J. Algebra 135.2 (1990), pp. 388–394. [Nee92] A. Neeman. “The connection between theK-theory localization theo- rem of Thomason, Trobaugh and Yao and the smashing subcategories of Bousfield and Ravenel”.Ann. Sci. ´Ecole Norm. Sup. (4)25.5 (1992), pp. 547–566. [NS16] A. Nyman and S. P. Smith. “...
work page internal anchor Pith review Pith/arXiv arXiv 1990
-
[25]
Categorical mirror symmetry: the el- liptic curve
Progress in Mathematics. Birkh¨ auser Verlag, Basel, 1999, pp. vi+261. [PZ98] A. Polishchuk and E. Zaslow. “Categorical mirror symmetry: the el- liptic curve”.Adv. Theor. Math. Phys.2.2 (1998), pp. 443–470. [RBN19] A. Rizzardo, M. Van den Bergh, and A. Neeman. “An example of a non-Fourier-Mukai functor between derived categories of coherent sheaves”.Inven...
work page 1999
-
[26]
The derived category of blocks with cyclic defect groups
CMS Conf. Proc. Amer. Math. Soc., Providence, RI, 1998, pp. 467–480. [Rou98] R. Rouquier. “The derived category of blocks with cyclic defect groups”. Derived equivalences for group rings. Vol
work page 1998
-
[27]
The stable homotopy category has a unique model at the prime 2
Lecture Notes in Math. Springer, Berlin, 1998, pp. 199–220. [Sch01] S. Schwede. “The stable homotopy category has a unique model at the prime 2”.Adv. Math.164.1 (2001), pp. 24–40. [Sch07] S. Schwede. “The stable homotopy category is rigid”.Ann. of Math. (2)166.3 (2007), pp. 837–863. REFERENCES 25 [Sch10] S. Schwede. “Algebraic versus topological triangula...
work page 1998
-
[28]
An exact sequence interpretation of the Lie bracket in Hochschild cohomology
London Math. Soc. Lecture Note Ser. Cambridge Univ. Press, Cambridge, 2010, pp. 389–407. [Sch98] S. Schwede. “An exact sequence interpretation of the Lie bracket in Hochschild cohomology”.J. Reine Angew. Math.498 (1998), pp. 153–
work page 2010
-
[29]
TheA ∞ deformation theory of a point and the derived categories of local Calabi-Yaus
[Seg08] E. Segal. “TheA ∞ deformation theory of a point and the derived categories of local Calabi-Yaus”.J. Algebra320.8 (2008), pp. 3232–
work page 2008
-
[30]
A ∞-subalgebras and natural transformations
[Sei08] P. Seidel. “A ∞-subalgebras and natural transformations”.Homology Homotopy Appl.10.2 (2008), 83?114. [Sei10] P. Seidel. “Suspending Lefschetz fibrations, with an application to local mirror symmetry”.Comm. Math. Phys.297.2 (2010), 515?528. [Sei15] P. Seidel. “Homological mirror symmetry for the quartic surface”. Mem. Amer. Math. Soc.236.1116 (2015...
work page 2008
-
[31]
Une structure de cat´ egorie de mod` eles de Quillen sur la cat´ egorie des dg-cat´ egories
[Tab05] G. Tabuada. “Une structure de cat´ egorie de mod` eles de Quillen sur la cat´ egorie des dg-cat´ egories”.C. R. Math. Acad. Sci. Paris340.1 (2005), pp. 15–19. [To¨ e07] B. To¨ en. “The homotopy theory ofdg-categories and derived Morita theory”.Invent. Math.167.3 (2007), pp. 615–667. [Ver96] J.-L. Verdier. “Des cat´ egories d´ eriv´ ees des cat´ eg...
work page 2005
-
[32]
American Mathematical Society, Providence, RI, 2013, pp
Graduate Studies in Mathematics. American Mathematical Society, Providence, RI, 2013, pp. xii+618. (Jasso, Schroll)Mathematisches Institut, Universit ¨at zu K ¨oln, Weyertal 86-90, D- 50931 K ¨oln, Germany Email address:gjasso@math.uni-koeln.de URL:https://gustavo.jasso.info Email address:schroll@math.uni-koeln.de URL:https://sites.google.com/site/sibylle...
work page 2013
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