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25 votes
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Jon Beck's untitled manuscript containing the "tripleability theorem" (i.e. the monadicity t...

After reaching out to every researcher who cited the manuscript, John Kennison was kind enough to find and scan his copy of the untitled manuscript containing the crude and precise monadicity theorems …
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17 votes
2 answers
1k views

Jon Beck's untitled manuscript containing the "tripleability theorem" (i.e. the monadicity t...

Many papers refer to an untitled manuscript of Jon Beck (Cornell, 1966) for the origin of the monadicity theorem (originally called a "tripleability theorem"). An early proof is in Manes's 1967 thesis …
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11 votes
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Reference request for Linton's theorems on equational theories

Dubuc establishes an equivalence between (large) $\mathcal V$-theories and $\mathcal V$-monads on $\mathcal V$, which in particular implies the classical result. … I haven't found an earlier reference with proofs. (1, 2, 3) As far as I am aware, the only paper in which both results follow directly is Lucyshyn-Wright's Enriched algebraic theories and monads for a …
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11 votes
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Double category of algebras, lax and colax morphisms of algebras

The double category of pseudoalgebras, lax and colax morphisms is defined in §5.4 of Grandis and Paré's Multiple categories of generalised quintets. As far as I'm aware, it is the only reference for t …
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10 votes
1 answer
325 views

2-monads for categories with a class of (co)limits

Power–Cattani–Winskel's A Representation Result for Free Cocompletions in particular seems promising, but the characterisation result there still assumes that such 2-monads exist in the first place. …
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9 votes
0 answers
102 views

Cocompleteness of enriched categories of algebras

A useful result due to Linton is that for a cocomplete category $C$ and monad $T$ on $C$, if the category of algebras $C^T$ admits reflexive coequalisers, then it is cocomplete (see here for a sketch …
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9 votes
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Eilenberg-Moore category as a 2-dimensional limit

Yes, the Eilenberg–Moore object for a monad $T$ can be presented in terms of two equifiers of the inserter $\mathbf{Ins}(T, 1)$. Denoting by $\phi \colon TU \Rightarrow U$, we equify $1_U$ and $\phi \ …
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9 votes
1 answer
347 views

Algebraically-free monadicity theorem

Is there an intrinsic characterisation of those monads on $\mathbf E$ that are algebraically-free? …
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9 votes
0 answers
186 views

What is the relationship between free bicompletion and the Isbell envelope?

Given a small category $\mathbb C$, we can form the free cocompletion $\mathbf y : \mathbb C \to \mathcal P(\mathbb C)$ and the free completion $\mathbf y^\circ : \mathbb C \to \mathcal P^\circ(\mathb …
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8 votes
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When is the Eilenberg-Moore category of a monad on an ind-category itself an ind-category?

Let $T$ be a monad on an accessible category (i.e. an $\mathbf{Ind}$-category). If the underlying endofunctor of $T$ is finitary (i.e. preserves filtered colimits), then the Eilenberg–Moore category o …
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7 votes
1 answer
215 views

Free idempotent monad associated to a monad

There is a full subcategory $\text{IdemMnd}(C) \hookrightarrow \text{Mnd}(C)$ of the category of monads on $C$ spanned by the idempotent monads. …
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7 votes
1 answer
551 views

Characterisation of essentially algebraic theories as monads

The category of (finitary) $S$-sorted algebraic theories is equivalent to the category of (finitary) monads on $\mathbf{Set}/S$. … The category of (finitary) $S$-sorted essentially algebraic theories is equivalent to the category of [some class of] monads on [some category]. …
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7 votes
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Relative cocompletion of a category

This is a special case of the general construction of cocompletions that preserve existing colimits. The general statement can be found as Theorem 6.23 of Kelly's Basic Concepts of Enriched Category T …
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7 votes
0 answers
159 views

Coherence for pseudomonads and their pseudoalgebras

That is, can we always choose to work with 2-monads rather than pseudomonads, so long as we consider their pseudoalgebras, rather than their strict algebras? …
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6 votes
0 answers
120 views

Original reference for the correspondence between commutative algebraic theories and commuta...

Commutative monads were introduced by Kock in the 1970 paper Monads on symmetric monoidal closed categories. … Though Kock cites Linton's paper, I could find no reference to commutative algebraic theories in any of his papers on commutative monads. …
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