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Adjunction contexts and regular quasi-monads | Robert Wisbauer
; | Date: |
6 Jan 2011 | Abstract: | Generalising the unit element in a ring, one may consider (central)
idempotents in the ring. Similarly, the unitality condition required for a
monad $(F,mu,eta)$ on any category was released (by G. B"ohm et al.) to
define {em pre-monads} by imposing weaker requirements on $eta$. Doing so,
the adjointness of the free functor from $A$ to the category of unital
$F$-modules $A_F$ and the forgetful functor is lost. In this paper we
establish, for a premonad $(F,mu,eta)$, a weakened form of adjointness
between the free functor from $A$ to the category $
A_F$ of {em regular
quasi-$F$-modules} with the forgetful functor.
For this we consider, for functors $L:A o B$ and $R:B o A$ between any
categories $A$ and $B$, an {em adjunction context} given by maps
$$xymatrix{Mor_B (L(A),B) ar@<0.5ex>[r]^alpha & Mor_A
(A,R(B))ar@<0.5ex>[l]^eta,}$$ natural in $Ain A$ and $Bin B$. We call
this a {em regular adjunction context} if both $alpha$ and $eta$ are
regular, that is
$alpha = alphacirc etacirc alpha$ and $eta = eta
circalphacirceta$.
From this configuration we derive the notion of a {em regular quasi-monad}
and a {em regular quasi-comonad} leading to {em pre-units} and {em
pre-monads} (as considered by G. B"{o}hm, J.N. Alonso ’Alvarez, and others).
The notions allow to study the lifting of functors between categories to the
corresponding categories of regular quasi-modules.
Along the way, the corresponding notions for {em quasi-comonads} are
formulated. The entwinings of regular quasi-monads and quasi-comonads
considered in the final section provide the techniques to handle {em weak
bialgebras} and {em weak Hopf algebras} on arbitrary categories but this
aspect is not exploited in the present paper. | Source: | arXiv, 1101.1195 | Services: | Forum | Review | PDF | Favorites |
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