The fibre functor is symmetric monoidal #
Deligne's ω is base change to the algebra followed by
realization, and its monoidal comparison RS.fibreMu is, on the
generators of the tensor product of super modules, nothing but the
free-module shuffle evaluated at a pair of morphisms. The three
coherence laws of a lax monoidal functor therefore reduce, family
by family, to the three coherence laws of the shuffle recorded in
RS.FreeModShuffleCoh.
The reduction is uniform. Each generator family names a morphism
s out of the intended source into a tensor product of the two
sources involved, and the comparison sends a pair (m, n) to
s ≫ (m ⊗ₘ n) ≫ freeModShuffle. Associativity at a family is
then the associativity of the shuffle conjugated by the coherence
identity relating the four s's of that family — exactly the
identity that already appears in the corresponding associativity
axiom of RS.gammaModule. Unitality and the braiding law are the
same computation one factor shorter.
Two signs appear, and both are forced by the target rather than by the fibre functor:
- the Koszul sign of
rightUnitorHom_evenMap_tmulOOin the odd-odd family of the right unitor; - the Koszul sign of
braidingHom_evenMap_tmulOOin the odd-odd family of the braiding.
In both places the sign is supplied by RS.OddLine.braid_neg: the
self-braiding of the odd line is −1, so the source identification
L.sq.inv picks up exactly that sign when the two odd generators
are exchanged. No sign is left over.
The functor is packaged as CategoryTheory.Functor.LaxMonoidal and
CategoryTheory.Functor.LaxBraided. Invertibility of fibreMu is
a separate matter and is not assumed here, so the strong notions
Functor.Monoidal and Functor.Braided are not instantiated.
Splitting a tensor of composites #
A composite in the first factor, split off on the left.
A composite in the second factor, split off on the left.
A composite in the first factor, split off on the right.
A composite in the second factor, split off on the right.
The coherence of the shuffle at arbitrary sources #
Associativity of the shuffle at arbitrary sources. Given a coherence identity between the two ways of reassociating the chosen sources, the two ways of shuffling three morphisms agree.
RS.freeModShuffle_assoc_at, bracketed as realization of the
reassociation of the generators produces it.
Left unitality of the shuffle, with the trailing reassociation of the generators cancelled.
Left unitality of the shuffle at arbitrary sources: filling the first slot with the unit comparison leaves the action of the free module.
RS.freeModShuffle_unit_left_at, bracketed as realization of
the left unitor of the generators produces it.
Right unitality of the shuffle, with the trailing reassociation of the generators cancelled.
Right unitality of the shuffle at arbitrary sources: filling the second slot with the unit comparison leaves the action of the free module, the two sources having been exchanged.
RS.freeModShuffle_unit_right_at, bracketed as realization of
the right unitor of the generators produces it.
The shuffle commutes with the braiding, at arbitrary sources.
RS.freeModShuffle_braiding_at, bracketed as realization of
the braiding of the generators produces it.
The braiding on the four sources #
The even-even source is fixed by the braiding.
The braiding exchanges the even-odd and odd-even sources.
The braiding exchanges the odd-even and even-odd sources.
The four families of the unitor and the braiding #
Right unitality at the even-even family.
Right unitality at the odd-odd family; the Koszul sign of the right unitor appears here, and nowhere else.
Right unitality at the even-odd family.
Right unitality at the odd-even family.
The braiding at the even-even family.
The braiding at the odd-odd family; the Koszul sign of the Koszul swap appears here, and nowhere else.
The braiding at the even-odd family.
The braiding at the odd-even family.
The fibre functor and its comparison data #
The fibre functor over an algebra: base change to the algebra followed by realization.
Equations
- RS.fibreOver L R = (RS.freeModFunctor R).comp (RS.gammaModuleFunctor L R)
Instances For
Realization of a base-changed morphism, in even degree.
Realization of a base-changed morphism, in odd degree.
Associativity #
Associativity of the monoidal comparison of the fibre functor: the two ways of comparing a threefold tensor product agree, up to the associator of the super modules and the reassociation of the three objects.
Unitality #
Left unitality of the monoidal comparison of the fibre functor: the unit comparison in the first slot is the left unitor of the super modules. No sign appears.
Right unitality of the monoidal comparison of the fibre
functor: the unit comparison in the second slot is the right
unitor of the super modules. The Koszul sign of the odd-odd block
of the right unitor is RS.freeModShuffle_unit_right_oo, and it is
supplied by RS.oddLine_sq_inv_braiding.
Compatibility with the braiding #
The monoidal comparison of the fibre functor commutes with
the braiding: swapping the two factors of the super-module
tensor product and comparing agrees with comparing and swapping
the two objects. The Koszul sign of the odd-odd block of the
Koszul swap is RS.freeModShuffle_braiding_oo, and it is again
supplied by RS.oddLine_sq_inv_braiding.
The lax monoidal and lax braided structures #
The fibre functor is lax monoidal, with unit RS.fibreEps
and tensorator RS.fibreMu.
Equations
- RS.fibreOverLaxMonoidal L R = CategoryTheory.Functor.LaxMonoidal.ofTensorHom (RS.fibreEps L R) (RS.fibreMu L R) ⋯ ⋯ ⋯ ⋯
The unit of the lax monoidal structure.
The tensorator of the lax monoidal structure.
The fibre functor is lax braided: its tensorator commutes with the two symmetries.
Equations
- RS.fibreOverLaxBraided L R = { toLaxMonoidal := RS.fibreOverLaxMonoidal L R, braided := ⋯ }